Charest said the two provinces share many common interests.
"When you're abroad, in China, and they (the Chinese) see...the two provinces working together and being on the same page, that makes us more interesting," he said. "It helps Ontario and Quebec projects.
"It goes without saying that it is in our interest to be side by side instead of apart."
He made the comments in Beijing where he attended a banquet with three current premiers who are on a trade mission in China: Quebec's Philippe Couillard, Ontario's Kathleen Wynne and Prince Edward Island's Robert Ghiz.
Charest, who visited China during his tenure as premier between 2003 and 2012, said he believes the election of Liberal majority governments in Quebec and Ontario this year has "breathed new life" into the provinces' relationship as well as the Council of the Federation.
Earlier in the day, Couillard, Wynne and Ghiz met with Jiang Daming, who oversees 400,000 employees as China's territories and resources minister.
Couillard used the get-together to promote his ambitious plan to develop northern Quebec.
"We will present the Plan nord to Chinese businesses so that they can become more involved with its development," Jiang said later through an interpreter.
"We hope that both parties can make it easier for them to work together."
That was music to Couillard's ears.
"I was very happy to hear that," he said. "The fact he wants to promote it among the rest of the government is very, very important for us."
Three Chinese firms are already involved in mining projects in northern Quebec.