The investment firm said the profit amounted to 25 cents per share in its latest quarter compared with a profit of 34 cents per share a year ago.
CI said the one-time future tax charge was $18.8 million and excluding the charge it would have earned 32 cents per share for the quarter.
Assets under management for the quarter totalled $71.6 billion, down from $74.3 billion a year ago.
Selling, general and administrative costs were down six per cent compared with the second quarter of 2011.
"CI has performed very well in an incredibly challenging environment," president and chief executive Stephen MacPhail said in a statement.
"CI's earnings were resilient, with a decline of just a penny per share excluding the punitive effect of the Ontario government's tax changes, which reduced CI's income by 22 per cent in the quarter."
Shares in the company were up six cents at $22.48 in trading on the Toronto Stock Exchange on Thursday.