中文摘要：

公司透明度是资本市场有效运行的基础条件，并构成一个经济体的基本信息环境。股改作为上市公司的基础性制度变迁，将对公司治理结构与资本市场运行的信息环境产生重大影响。本文旨在从透明度改进角度，探讨股权分置改革的有效性。研究结果表明，作为基本信息环境透明度的指标，无论是盈余激进度、盈余平滑度还是其综合透明指数，其平均值在2003—2006年间，都呈现出逐年降低趋势，尤其是股改后各不透明度指数下降幅度更大。股改有效地降低盈余激进度和盈余平滑度，从而改进公司透明度，提升资本市场有效性。

英文摘要：

Corporate transparency is the basis for the capital market to run effectively. It also constitutes the fundamental information environment of the economy. As the basic institutional change of the listed companies, the stock split structure reform will have significant influences on the information environment which the corporate governance structure relies on and in which the capital markets run. This article discusses the effectiveness of the reform from the perspective of transparency improvement. The results indicate that whether the earnings aggressiveness, or earnings smoothness, or their comprehensive transparency index, all of their respective averages show a declining trend during 2003-2006, especially after the reform. The reform can effectively decrease the earnings aggressiveness and earnings smoothness, so as to improve the corporate transparency and promote the effectiveness of the capital market.