The equilibrium theory of island biogeography describes that the number of species on an island is determined by two factors, island area and distance from mainland acting through extinction and immigration rates. I was analysed the relationships between species number and island area, latitude, and maximum elevation for butterflies on 71 islands in the Korean Peninsula. Among Korean islands, island area ($r^2$=0.405, P< 0.005) and habitat diversity ($r^2$=0.341, P<0.005) were significantly correlated, but distance from mainland ($r^2$=0.018, P>0.05) and latitude ($r^2$=0.040, P>0.05) were weakly correlated. The present and earlier studies on the butterfly species richness in Korean islands demonstrate that the butterfly fauna is closely related to the ecological variables, i.e., area, composition of flora and maximum elevation. [Equilibrium theory, butterfly, island area, latitude, distance from mainland, elevation]