Isotactic poly(l-butene) (PB-1) films, consisting either of crystal form III (solution-grown crystal mat) or I＇ (melt-crystallized film under a high pressure), were drawn uniaxially by tensile draw and solid-state coextrusion in the range of room temperature to 80 degrees C, below their melting temperatures (T-m = 90-100 degrees C). The phase transformations induced by draw were characterized by WAXD and DSC. The results are discussed in terms of the effect of drawing variables on the deformation mechanism of PB-1. Tensile draw, which proceeded with a clear neck, was variable and affected by the initial crystal forms and draw temperatures. Upon the tensile draw of form I＇ films, oriented unstable form II crystals were formed independently of draw temperatures. They spontaneously transformed into the stable form I, as reported. When the form III mat was tensile drawn at 80 degrees C, near its T-m, oriented form II crystals were obtained, whereas the draw at a lower temperature of 70 degrees C produced oriented form I＇ crystals. Crystal form II is known to form only by crystallization from the random chain conformation, including melt, glass, and solution. Thus, the formation of the form II on tensile draw suggests that the deformation had proceeded thorough quasi-melting followed by recrystallization into the oriented form II. In contrast to the tensile draw with a neck, solid-state coextrusion, where the deformation proceeds gradually within an extrusion die, produced oriented form I＇ crystals independently of the initial crystal forms and extrusion temperatures. This suggests that the deformation on solid-state coextrusion proceeded in the crystalline state. These results indicate that the draw of PB-1 proceeds either through quasi-melting/recrystallization or in the crystalline state depending on the draw technique and temperature and the crystal form of the initial starting sample.