In the present paper, a link-arrangement system for spatial mechanisms with consideration of mutual interferences among moving links is investigated. In order to determine optimum profiles of links which satisfy the minimum moving space of the mechanisms, a rotary plane which arbitrary fixed on one of the moving link in the mechanism is introduced, and relative loci of pairing points and positions of links with this plane are analyzed. Moreover, conditions to determine link arrangements avoiding mutual interferences of moving links are formulated. Based on the above analytical results, a link-arrangement system is constructed which obtains the optimum profiles and arrangements of links of spatial mechanisms. Applying the system, a spatial 4-bar mechanism is synthesized as a practical example.