Peritectic solidification was studied using Sr(NO3)2-H2O system where Sr(NO3)2 (α phase) , Sr(NO3)2.4H2O (β phase) and H2O (γ phase) crystallize: the phase relations of the first and the last two are peritectic and eutectic, respectively. Three solutions with composition C1, C2 and C2 where α, β and γ respectively equilibrate with liquid phases were kept at several temperatures to observe the solidification processes under an optical microscope. With decreasing temperature, α, β and γ phases nucleated in this order in the solution C1. It is noted that β phases nucleated heterogeneously on the preexisting α phases. In the three solutions with the lower temperatures, γ and then α and occasionally β phases appeared to complete solidification. It is concluded that the favorable growth of β phase on α phase results in peritectic texture in any solution although the texture consisting of β and γ phases only is not formed.