Under weak form efficiency the assertion is that stochastic modeling of past data is useless since random walk processes generate short-term price movements.

This paper examines the weak form efficiency in Shanghai stock market from the beginning of 1991 to the end of 1996 by applying modern investment theories and empirical research method.

The results show that whereas the A-share markets were inefficient before spilt share reform, they have reached the weak-form efficiency after that.