Asos founder and non-executive director Nick Robertson has sold 300,000 shares, worth more than £15.5m.
The shares were sold at an average price of just over 5,175p each.
Following the disposal Robertson, who stepped down from his role as chief executive in September 2015, still owns more than five million shares in Asos, representing 6.23% of the firm.
Asos’ market cap is currently £4.4bn.
Retail sales at Asos soared by 36% on a reported basis (30% on a constant currency basis) to £605.7m in the four months to 31 December.