The stock filing to the Hong Kong exchange indicates that Ma, who co-founded Tencent in 1998, sold a total of 25.11 million shares during December 2 and 5 at prices ranging between HK$119 and HK$120, cashing in HK$3 billion ($387 million), according to a NetEase news report on Tuesday morning.
The selling prices are not "desirable" ones, which represent discounts of around 12 percent over its previous peak of HK$134.90 per share, recorded on November 17 this year, previous data shows.
Ma's stake in Tencent has declined to 9.87 percent from 10.13 percent prior to the sale. He remains the company's largest individual shareholder, but it is for the first time that his stake has dropped below 10 percent, said the report. Ma's previous sales of Tencent shares began in 2011, but occurred on a smaller scale.
A spokesman from the Shenzhen-based company said the sale was for Ma's personal wealth management purposes, Hong Kong media reported on Wednesday.
Markets suspect that Ma Huateng, together with Ma Yun -- the founder and executive chairman of Alibaba Group -- had participated in Ping An Insurance's HK$37 billion ($4.8 billion) private placement in Hong Kong in late November.
The 2014 Forbes China Rich List released last month ranked Ma Huateng as the third-richest person on the Chinese mainland -- up from fifth place in 2013, with a fortune of $14.4 billion compared with $10.2 billion a year ago.
Ma Huateng's Tencent reaped huge profits from online games, alongside free messaging services. The company's instant messaging app WeChat has nearly 440 million users, said the Forbes report.