This chapter analyzes the determinants of party systems in Japanese prefectural legislatures. We can classify four types of prefectural legislatures. The first is one-party dominant type. The effective-number of parties in such prefectures has been constantly under two. The second type resembles the party system of national diet before 1994. Their ENP has been stable between two and three. Some prefectural legislatures have been highly fragmented so that their ENP goes up more than three. In the fourth type, we see that party systems are highly disunited after late 1990s. We explain these differences among prefectures and time-series changes by electoral institutions, relations between legislators and governors, and relations between national and local party members. Statistical analyses on time-series cross sectional data of postwar 47 prefectures reveal that large magnitude of electoral districts, independent governors, non-concurrent elections of legislators and governors, and fragmented national level party systems in the prefecture cause the fragmentation of party systems in the prefectural legislatures.