台灣在1920年代底，農地租約所處的外在環境開始歷經重大的轉變。一 方面租佃糾紛持續增多;另一方面業佃改善團體出現，除了規定會員採用業佃會 書式租約，也堤供會員高效率的租佃糾紛調停服務。相應於此，租約的結構也在 1930年代發生根本的改變:從口頭契約占絕對優勢的型態演變為業佃會書式契約 居絕對優勢之結構。當口頭契約盛行之際，書面契約大多只行之於新開墾地、造 成茶園、造成果園、大片土地、公業地、不在地地主、會社、或業佃互信程度低 的場合。而當書面契約盛行之際，口頭租約也依然行之於租期很短、業佃關係特 別好、或面積很小之租佃地的場合。本文發現各時代所呈現的租約結構或其轉變 的方向，大致符合理性選擇行為的準則。

　　　　　The context within which farm rental contracts were made in Taiwan has dramatically changed after the end of the 1920s. On the one hand, disputes between landlords and tenants increased significantly. On the other hand, landtenure improvement associations were created ro offer quite efficient mediationservices. In response) the structure of rental contracts fundamentally changedduring the 1930s: changing from a pattern dominated by oral contracts ro a pattern dominated by written contracts designed by the land tenure improvementassociations. This article shows that the structure of rental contracts as they appeared in each era and the manner in which they changed were consistent with economic rationality.