The structural parameters such as long spacing and thicknesses of crystalline lamellae and amorphous layers of polybutene-1 crystallized from quiescent melt at different isothermal temperatures and established by tensile stretching the isothermally crystallized samples at different temperatures via a stress induced localized melting and recrystallization process were determined by small-angle X-ray scattering experiments. In the two cases, almost parallel crystallization lines where reciprocal lamellar thickness and temperature at which the structure formed are in linear relationship were observed. As it turns out, the samples crystallized from the quiescent melt possess much thicker crystalline lamellae than those obtained via stretching at same temperature. The results yield two limiting temperatures for the formation of lamellae with infinite thickness in the two cases which can be understood by considering the influence of the stress on the thermodynamic parameters in the melt and thus the crystallization process.