This thesis examines the Indonesia foreign policy towards Malaysia, specifically in the case of Ambalat and Indonesian workers (TKI). This study is important due to some changes in the Indonesian foreign policy towards Malaysia that have occurred in last few decades. The changes were significantly impacted to the rise of the tension between the two countries especially in the both cases. Generally, this study attempts to answer three main questions namely (i) how has the changes in Indonesian foreign policy towards Malaysia?; (ii) how has the changes in Indonesian foreign policy towards Malaysia in the case of Ambalat and Indonesian workers (TKI)?; (iii) to what extent has the impact of international structure on the changes of the pattern and behavior of Indonesian foreign policy towards Malaysia in the case of Ambalat and Indonesian workers (TKI)?. Therefore, using Defensive Realism, this study has three main objectives (i) to discuss the trend of Indonesian foreign policy towards Malaysia in the context of the Indonesia-Malaysia bilateral relations; (ii) to analyze the Indonesian foreign policy towards Malaysia in the case of Ambalat and Indonesian workers (TKI) and the influence factors; (iii) to analyze the application of Defensive Realism to explain Indonesian foreign policy towards Malaysia in the case of Ambalat and Indonesian workers (TKI). The findings of this study demonstrated that the new international political structure after the end of the Cold War was tremendously impact to the Indonesian foreign policy towards Malaysia in the two cases. Nevertheless, other factors such as leadership, domestic politics competition, sentiment of nationalism and media provocation also give significant impact to the posture and behavior of Indonesian foreign policy towards Malaysia.