The effect of poly (lactic acid) (PLA) on the crystalline phase transition of poly (vinylidene fluoride) (PVDF) from - to -phase under uniaxial stretching for immiscible PVDF/ PLA blends was investigated. The typical sea-island structure in the blends was found to facilitate the necking of PVDF and the transition from - to -phase due to the local stress distribution during stretching. The crystalline phase transition of PVDF in the blends is temperature-dependent and is affected by the content of PLA. The highest content of -phase, F(), was achieved in the samples stretched at 60 degrees C, while the effect of PLA content on the crystalline phase transition of PVDF is more complex. F() increases slightly when the sample with a PLA content no more than 15 wt % is stretched at 60, 80, and 100 degrees C, and decreases sharply for the sample containing 20 wt % PLA; in addition, the sample containing 10 wt % PLA exhibits the highest F() no matter what the stretching temperature is. The mechanism of the crystalline phase transition of PVDF during the stretching is interpreted from energy barrier of the transition from - to -phase and the morphological structures in the blends. (c) 2012 Wiley Periodicals, Inc.