Former Google chief executive Eric Schmidt plans to sell up to 2.4 million shares of stock currently worth nearly 1.5 billion dollars (£949m).
Mr Schmidt, now Google's executive chairman, intends to stagger the sales of the stock over a year.
Google disclosed his plans in a regulatory filing.
The company said Mr Schmidt, 56, was trying to raise some money and diversify his investment portfolio.
If all 2.4 million shares of stock are sold, that will reduce his stake in Google from 2.8% to 2.1%.
Mr Schmidt's decision to sell some of his shares comes 10 months after he ended his 10-year stint as Google's chief executive and turned the job over to one of the internet search leader's co-founders, Larry Page.
Mr Page and co-founder Sergey Brin filed plans to sell five million Google shares apiece in 2010. Those sales are due to be completed in 2015.
Together, Mr Page, Mr Brin and Mr Schmidt hold the majority of shareholder voting power at Google. They will retain that control even after they reduce their stakes. All three have been billionaires since Google went public in 2004.
Google shares fell 1.88 dollars on Friday to close at 604.64. The company disclosed Mr Schmidt's plans to lower his holdings after the stock market closed. The shares fell 44 cents after hours.