The crystalline lattices of random poly(3-hydroxybutyrate-co-3-hydroxyvalerate) were found to be independent of the crystallization temperature, whereas the composition in the crystalline phase changes. The rise in the crystallization temperature is accompanied by the decrease in the content of minor comonomer units in the crystalline phase. The relationship between the composition in the crystalline phase and the melting point is consistent with the expectation from the phase diagram proposed in a previous paper