In January 1983, Japan finalized an economic assistance agreement with the Republic of Korea (ROK) pledging to extend $4 billion economic aid to the country concerned. Prior to the finalization of the said agreement, both countries held rounds of negotiation on the aid package conditions and, this led them entering into a period of growing political frictions.<br> Despite this, nonetheless, a political consensus was eventually hammered out in 1983 over their disagreement and this had far-reaching impacts in stabilizing the political relationship between both countries. Doubtlessly, numerous intellectual researches have been consistently conducted in the above field of studies. Nevertheless, the reasons behind Japan’s commitments to rounds of political negotiation with ROK have yet to be positively analyzed and convincingly substantiated.<br> Against this premise, the main aim of this article is to analyze the motivational forces that brought Japan to the negotiating table with ROK. More specifically, it focuses on analyzing the impacts of the formalization process of the Japan-U.S. agreement that served to induce Japan to address the ROK-aid negotiation issue conscientiously.<br> The analysis reveals clearly that the major factor that spurred Japan to revisit its ROK’s aid package conditions was its concern over the security burden-sharing scheme with U.S. It may well be that in July 1981, Prime Minister Suzuki Zenko in his summit meeting with President Ronald Reagan pledged to initiate official talks with ROK in response to its request for an extended economic aid package.<br> In tracing the course of Japan-U.S.’s political negotiations from the period between 1977 prior to the formalization of ROK’s aid agreement, the analysis distinctly reveals that both countries were politically in consensus on need of the agreement as a one of the critical means to resolve a myriad of their security burdens. Nonetheless, it is further disclosed that both countries derived at their ROK’s aid consensus from different perspectives that were politically beneficial to their own countries concerned.<br> On the one hand, the U.S. expected Japan to assume greater responsibilities on security burden sharing in line with its global economic status. On the other hand, partly because of its political limitation in shouldering a regional security role, Japan’s primary concern was to minimize its economic burdens as far as possible and in such way as not to disrupt its harmonious security relationship with U.S.<br> On top of this, insofar as U.S. was concerned, it seemed to be unwise to request Japan to overshare the bilateral security defense expenditure which might be detrimental to its political stability at home and which at the same time affecting the credibility of their security alliance relationship.<br> In a nutshell, the article explicitly shows that the Japan-U.S. ROK’s aid consensus was beneficial to both countries in term of resolving their differences in the political operation of their security alliance scheme including burden sharing responsibilities. This is indeed the real factor behind Japan’s commitment to revisit its economic aid package with ROK.