By Trevor Hunnicutt

NEW YORK, July 13 (Reuters) - BlackRock Inc voted for eight proposals pushing U.S. and Canadian companies to adopt policies boosting their boards' diversity during the most recent quarter, the world's largest asset manager said on Thursday.

BlackRock said it supported the shareholder motions to press companies to develop or disclose policies geared to promote gender diversity. It did not name the companies it pushed but said the "majority" had boards of directors lacking women.

"We've been particularly focused on increasing the number of women on U.S. boards because progress in the U.S. has been slower than in many other markets," BlackRock said in a report it distributed.

"Board diversity, particularly in terms of gender, is important from a sustainable investment perspective, given that diverse groups have been demonstrated to make better decisions," it added.

"This appears to be because they are better able to consider, where appropriate, alternatives to current strategies - a proposition that can ultimately lead to sustained value creation."

Women hold about a fifth of board seats in the S&P 500 index, according to Catalyst Inc, an advocacy group.

BlackRock said it also voted against board members at five companies who sat on nominating committees but failed to respond to investors' concerns about diversity.

It was the first year the company "decided to vote against members of the nomination committee of men-only boards in a more systematic manner," a spokesman said, although it had engaged on the topic of gender diversity for "many years."

The New York-based company manages more than $5.4 trillion in assets, many in index funds that buy broad swaths of the market, making it a top shareholder in most public companies.

It has been pressured by activists and investors to back shareholder-fronted propositions and vote against obstinate boards to prompt better corporate citizenship.

Chief Executive Larry Fink has encouraged executives to adjust their behavior to focus on generating long-term value for shareholders, rather than meeting short-term earnings targets.

Breaking with prior practice, BlackRock this year publicly disclosed opposition to practices at oil company Exxon Mobil Corp, drugmaker Mylan NV and other firms over climate change, compensation and other policies.

BlackRock's own board includes 17 members, four of whom are women. (Reporting by Trevor Hunnicutt; Editing by Clarence Fernandez)