Phase morphology, miscibility and thermal properties of a binary blend, poly(trimethylene terephthalate) (PTT) / polyamide-12 (PA12), were examined and found to be immiscible showing a phase-separated morphology. DSC cooling data of the blends indicates that the melt crystallinity of PTT phase increases, with respect to pure state, upon blending with PA12 while that of polyamide phase declines in the presence of PTT phase implying that polyester molecules reduces the crystallization ability of polyamide phase. Also, PA12 in that blend where it is minor phase shows a fractionated crystallization. A significant cold crystallization exotherm supposed to be due to the reorganization of polymeric chains was exhibited by PTT phase in DSC second heating thermograms which its degree was raised upon blending with PA12. DMA graphs reveal a single tan 6 peak due to the fact that the glass transition of the respective constituents overlap and a single peak comes into view. Therefore, DMA can not be solely used to assess the miscibility in this system.