It says Harper has more than 357,000 followers, well behind the 33.5 million of Barack Obama and Pope Francis, at 7.2 million.
The so-called Twiplomacy study was conducted by the New York-based firm Burson-Marsteller, which bills itself as an "evidence-based" communications firm.
"Prime Minister Harper was the fourth world leader to sign up to Twitter in July 2007 in the footsteps of @BarackObama, however he only started to tweet in September 2008 asking his followers to 'check out the new Conservative Party website'," the report says.
"Although the tweets are written in first person he rarely writes the tweets himself."
It also says Harper doesn't engage frequently with others on Twitter. That would appear to include most other world leaders, including the U.S. president. Harper doesn't follow Obama's feed.
"Prime Minister Harper is not very conversational, only 2% of his tweets are @replies and 6% retweets," the survey said.
"Surprisingly @PMHarper only follows Russian Prime Minister @MedvedevRussia and Uganda's PM @AmamaMbabazi but does not follow his peer at the White House."
But as the study points out, Obama isn't any better.
He may be the most followed, and he follows a record 661,000 Twitter users, but how many other world leaders does he follow?
Two. Obama follows the prime ministers of Norway and Russia, Jens Stoltenberg and Dmitry Medvedev.
The survey says Harper tweets his "vision" of Canada in an "informal way" and sometimes lets followers "enter his personal life."
That latter observation appears to reference the January day when Harper used his account to chronicle "a day in the life" as prime minister.
Most recently, Harper's office used the 140-character social media tool to announce the new portfolios in last week's cabinet shuffle.
An hour before he unveiled his new cabinet, Harper's account began tweeting individual new portfolios in what was viewed by some pundits as a social media striptease.
Harper's office has not been willing to indicate who actually does his tweeting, saying the prime minister only "occasionally" posts himself.
"His Twitter account is also empathetic when needed, e.g. on the occurrence of natural disasters," said the Twiplomacy study.
"During the election campaign in 2011 he traded 140-character blows in a Twitter exchange with his opponent, Liberal Party leader Michael Ignatieff (@M_Ignatieff) who had challenged him to a one-on-one debate."
The study ranked the Obama's institutional @whitehouse account in third place with more than four million followers.
Curiously, the top five was rounded out by two politicians from Turkey, Prime Minister Recep Tayyip Erdogan and President Abdullah Gul with 3.7 million and 3.4 million followers respectively.
The study looked at 505 heads of state and government, foreign ministers and their institutions in 153 countries.
It also examined the use of Twitter by diplomats.
It said Foreign Affairs Minister John Baird was "a firm believer in the benefits of digital diplomacy."
Baird "personally tweets from his iPhone" in both official languages both "on key foreign politics issues, with Syria crisis playing a major role in his updates, and his institutional agenda, speeches and meetings but without leaving out his passion for the Ottawa Senators hockey team."
Like many others, the study noted that Baird did not have a high level of interaction.
"His engagement though is limited with only 10 @replies and 8% retweets."
The most connected person is Swedish Foreign Minister Carl Bildt, who is mutually following 44 peers. He is followed in the ranking by the European Union's Catherine Ashton who has 36 mutual connections.
The Foreign Affairs Department was criticized for its approach to digital diplomacy in another study released last month by the Canadian Defence and Foreign Affairs Institute.
Authored by Roland Paris, the director of the Centre for International Policy Studies at the University of Ottawa, the study said Canada is lagging behind the U.S. and Britain in digital diplomacy.
It criticized the "centralized control" that prevents diplomats from speaking publicly on social media without prior permission from Ottawa.
Paris said that approach "makes it virtually impossible for Canadian diplomats to engage in real-time substantive exchanges, which is the currency of the medium."
Paris argued that unless Ottawa loosens the restrictions, "Canada's voice will progressively fade in international affairs."
Deepak Ohbrai, Baird's parliamentary secretary, rebutted that criticism pointing out the government's recent initiative to engage ordinary Iranians directly over social media.
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