This paper provides some evidence in support of the information transmission hypothesis that the onset of SIMEXfs MSCI Taiwan index futures and TAIFEXfs Taiwan index futures has helped stabilize the volatility process of Taiwanfs spot market. We use daily data of Taiwanfs stock index from January 1995 to December 2000 to estimate a GARCH model before and after futures trading. Before futures trading, the effects of volatility shocks tended to be more persistent. After futures trading, the volatility process became more stabilized such that shocks are more quickly reflected in the system and the system reverts to its normal state relatively quicker. This is consistent with the hypothesis that the flow of information has accelerated with the opening of futures trading. In other words, Taiwanfs stock market has improved its efficiency in processing market information due to trading of futures contracts in SIMEX and in TAIFEX. To check the robustness of our result, other data set was employed - the over-the-counter market index. The study showed that using the over-the-counter data set revealed the consistent phenomena with using the Taiwan stock index. Namely, the introduction of futures trading on market volatility and information transmission has positive effects in the underlying assetfs market efficiency. Key words:GARCH Model, Information Transmission Hypothesis, Volatility, Futures market