This paper is to investigate the relationship between whistle-blowing practice and unethical behavior at the Royal Malaysian Customs Department in Putrajaya which represents the Royal Customs Department organizations in general. The study was also conducted to determine whether whistle-blowing practice would influence the efforts to reduce unethical behaviour among Jabatan Kastam Diraja Malaysia (JKDM) officers and members. Other than that, this study also intends to identify the level of unethical behaviour and the whistle blowing practice among the officers and members of the JKDM Putrajaya. A total of 300 questionnaires were distributed and only 182 questionnaires were quoted for the analysis. Data were analysed using the SPSS software. The findings show that, the level of unethical behaviours among officers and members of JKDM is low. The whistle-blowing practice is at a high level in accordance with the perception of officers and members of JKDM Putrajaya. Whistle-blowing policies that have been studied have insignificant value with the unethical behaviours in comparison with the whistle blowing practices that have a significant value and the value is moderate. In the multiple regression analysis, only the whistle-blowing practice has a significant value on the ethical behaviour. Hence, the management, policy maker and JKDM leaders should pay attention to the seriousness of the distribution mechanism or whistle-blowing as one of the efforts to combat the unethical behaviour among officers and JKDM members.