This article aims at investigating the significance of the draft provisions on piracy, commonly known as “Matsuda Draft,” submitted by Michikazu Matsuda, a Japanese lawyer-diplomat, to the League of Nations Committee of Experts in 1927, by examining the historic and legal background of the draft and Matsuda’s views on international law.

The Committee of Experts was established by the League in 1924 and consisted of international lawyers from various countries to select topics of international law to be codified. Matsuda Draft, together with the so-called Harvard Draft, is widely known among current scholars as an important precedent of the formulation of the concept of piracy in international law. However, it is still unclear how the draft was drawn up and what kind of historical significance it has for the relationship between Japan and international law in the interwar period. This study compares the original text, which was initially submitted by Matsuda to the Committee, with the final draft, and then clarifies the background to the drafting of this document and its historical significance.

Matsuda Draft was the first official attempt to formulate a definition of piracy. What is more important from the perspective of the history of Japan’s relationship with international law is that a Japanese international lawyer prepared a report on piracy, consolidated the various opinions expressed on it by the experts in the Committee, and reflected them into a draft treaty. This fact provides a basis to reconsider the conventional view that prewar Japan was reluctant or negative about the development of international law.