The Chinese A-shares market witnessed a great reform of non-tradable shares in 2006. Until the end of 2011, most non-tradable shares had experienced expiration of lock-up. Insiders who were prohibited to trade can trade frequently now. Insider transactions have become a new phenomenon which attracts much attention. Some empirical studies have found that owing to lax regulation, insider trading in the A-shares market is prevalent and serious, with high trading profitability for the average insider. To curb the profitability of insider transaction, regulators require public trade disclosure right after the completion of trade. In the A-shares market, insiders, including directors, supervisors, top managers and shareholders owning more than 5% of total shares, are required to disclose detailed trade information within two days after trade completion, but no definite punishment is stipulated for delayed disclosure. This paper is an empirical study of the enforcement of disclosure policy based on top managers’ trading data disclosed by companies listed on Shanghai Securities Exchange. 15 percent of the transactions were disclosed with delay, but no punishment was imposed, evidencing the slack enforcement of disclosure policy. In comparison, strict sanction was imposed on insiders who had other illegal insider trades, such as short swing trade or trade during sensitive periods around the announcement of important events. Furthermore, opportunistic motives underlie insiders’ postponement of disclosure. Compared to timely disclosed trades, delayed trades have significantly higher probability of continuous trades and illegal trades, such as short swing trades and trades during sensitive periods. Besides, delayed trades can significantly predict future stock returns, indicating greater probability of informed trading. The evidence shows that when insiders embark on illegal insider trading, they always choose to delay disclosure. Why can disclosure delay reduce the exposure risk of illegal trades? As investors always focus on updated trades for new information and regulators are more likely to penalize the latest illegal trades, disclosure delay can, to some extent, shield illegal trades from the attention of investors and regulators. Under the legislative environment where strict enforcement on insider trading and lax enforcement on disclosure delay coexist, insiders may strategically reduce the exposure risk of insider trading and expand trading profitability through violating disclosure policies. An analysis of the economic consequences of disclosure delay shows that it negatively affects market price discovery. This paper has important implications for disclosure regulation. Due to the slack enforcement of disclosure policy, disclosure delay has become an opportunistic means for insiders to enlarge trading profitability and carry on illegal trades, and therefore has become a loophole of regulation, weakening regulation effectiveness. How do regulators and insiders interact? What is the internal mechanism of regulation policies and how does the enforcement of policies influence insider trading? These issues have long been the focus of academic attention. This paper is the first to analyze the impact of imbalanced regulatory enforcement on insider trading behavior.