The bid-ask spreads and market depth are important indicators to measure liquidity, and they are also factors which influence investors’ decision-making of order-submission. Transparency means the amount of investors acquiring transaction information, and it may be an important impact factor of bid-ask spreads and market depth which in turn, affect the behavior of investors on order-submission decision. This study investigates the effect of new trading regulation that Taiwan Stock Exchange (TSE) starts to disclose the information of the best five quotes and their corresponding orders on January 2, 2003. The result indicates that new trading regulation significantly reduces the bid-ask spreads and information asymmetric, but enhances the market depth and market liquidity only in those large firms.