This research is intended to see the characteristic of Insider trading breach at Indonesian Stock Market; the relevance of the regulations that govern the Insider Trading breach; and mechanism of law enforcement in handling the insider trading breach, particularly in the case of Stock Trading of PTINDOSAT Tbk. This research constitutes normative research that employs law comparative method. The starting point of this analysis is the investigation of the regulatory laws and the rules related with the law enforcement at Indonesian Stock Market. The analysis of this research results in the following conclusions ; 1. Regarding the characteristic of the violators, theoretically they may be qualified as traditional insider and temporary/quasi insider. Practically, the violators are often the management of the company. 2. The case of violation of the law on the stock market is sufficiently charged with the administrative sanction or further continued at the investigation level. It is due to characteristic of the Stock Market that is very unique and different from other financial institutions. Therefore, the stock market is prone to any issues or rumors. 3. In handling the case of insider trading, Bapepam encounters some hindrances, i.e : the lack of information that is very difficult to be proofed when it is not written or documented; the relation among me parties that do the transactions are difficult to be traced since the limited authority of Bapepam in disclosing the bank account of the customer; the strong indication of the involvement of the parties that have political ties that lead the reduced independence of Bapepam; Minimal budget owned by Bapepam so that the investigation team can not work maximally; the weak field coordination with the police and the public attorney. In the case of ISAT, it appears that in addition to the above factors, the information given by mass media is too fast so that every one could access it