In this article, the spherulitic growth rate of neat and plasticized poly(lactic acid) (PLA) with triphenyl phosphate (TPP) was measured and analyzed in the temperature range of 104-142 degrees C by polarizing optical microscopy. Neat PLA had the maximum value of 0.28 mu m/s at 132 degrees C, whereas plasticized PLA had higher value than that of neat PLA, but the temperature corresponding to the maximum value was shifted toward lower one with increasing TPP content. The isothermal crystallization kinetics of neat and plasticized PLA was also analyzed by differential scanning calorimetry and described by the Avrami equation. The results showed for neat PLA and its blends with various TPP contents, the average value of Avrami exponents were close to around 2.5 at two crystallization temperatures of 113 and 128 degrees C, the crystallization rate constant k was decreased, and the half-life crystallization time t(1/2) was increased with TPP content. For neat PLA and its blend with 15 wt TPP content, the average value of n was 2.0 and 2.3, respectively, the value of k was decreased, and the value of t(1/2) was increased with crystallization temperature (T-c). Further investigation into crystallization activation energy Delta E-a of neat PLA and its blend with 15 wt % TPP showed that Delta E-a of plasticized PLA was increased compared to neat PLA. It was verified by wide-angle X-ray diffraction that neat PLA and its blends containing various TPP contents crystallized isothermally in the temperature range of 113-128 degrees C all form the a-form crystal. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2980-2992, 2010