The Shanghai Composite suffered its largest one-day percentage fall during China's 2015 stock-market crash on August 24, 2015.
The index dropped 8.49% that day, in a session widely nicknamed Black Monday. The fall was part of a broader sell-off that followed a rapid rise in Chinese share prices and increasing concern about economic growth, corporate earnings, and the sustainability of market valuations.
Chinese authorities had already taken steps to support the market, including interest-rate cuts and changes affecting trading and margin finance. Those measures did not prevent renewed selling in August. Anxiety also spread internationally as investors interpreted the Chinese decline as a possible signal of weaker global demand.
The June 12 date marks the 2015 market peak for the Shanghai Composite, not its largest single-day percentage loss. The July 27 decline was also severe, but smaller than the August 24 fall.