This research aims to improve the thermal stability of Poly lactic acid (PLA) bioplastics by increasing the degree of crystallinity. The study is divided into two parts: The first part concentrates on the improvement of the heat resistance of PLA by using organic nucleating agents namely rice husk, rice flour and rice starches in comparison with talc, an inorganic nucleating agent. The influences of the various types and contents of 0.5-5 wt% nucleating agent were investigated; the addition of the organic nucleating agent of 0.5-1 wt% was found to accelerate the rate of crystallization of PLA. This was evident in the shifting down of the Tcc and a reduction of crystallization half time, which was reduced to about 20 minutes. Moreover, the organic nucleating agent also increased the degree of crystallinity by 4-8 times compared to that found in the pure PLA. Additionally, the thermal stability of PLA nucleated with all organic nucleating agents increased slightly to around 55-60 ºC. On the other hand, the addition of talc has more pronounced effect by increasing the HDT of PLA/Talc 5% up to 135 ºC, However, the cooling step of the injection process still takes time up to 5 minutes. Hence, the second part of the study was pursued to improve the thermal stability and to reduce the cooling time by annealing along with adding the nucleating agents. The cooling time was reduced to 1 minute and the HDT increased with greater annealing time, this was consistent with rise in the degree of crystallinity. The HDT of PLA with 1% talc was raised to 120 ºC and approximately 105 ºC for pure PLA, PLA /Rice husk 1% and PLA /Rice flour 1%. However, to increasing the HDT to more than 100 ºC for pure PLA, PLA /Rice husk 1% and PLA /Rice flour 1% would take 90 minutes while that of the PLA /Talc 1% takes only 10 minutes. The degree of crystallinity was also found to increase the modulus of PLA.