This article discusses characteristics of technological capabilities and the role of product architecture in capability building in the automobile parts industry in Japan. The product architecture is the scheme by which functional elements of a product are allocated to physical components. There are two modes of product architecture: a modular and an integral architecture. Major portion of automobile parts are based on the integral architecture, which requires complex and continual adjustments among interacting physical components as well as coordination of interactive activities between a focal assemblers and suppliers. This task nature encourages suppliers to build technological capabilities in a manner that advances adjustment and coordination functions. In the article two cases of suppliers are illustrated in detail—one produces fuel tanks and the other manufactures seats—in order to argue how they achieve coordination of interacting activities, and how the architecture influences processes that suppliers build technological capabilities.