The use of biodegradable polymers and their composites have wide applications and high demands because they can be ideal alternatives to non-biodegradable polymers due to the growing global environmental concerns. The biodegradation of PLA and starch-based plastic composites by the use of enzymes was studied in a commercial compost and soil. The composites were prepared from two biopolymers, i.e. polylactic acid (PLA) and starch, using Brabender 30 EHT mixer at the composition of 10:90, 25:75, 50:50, 75:25 and 90:10 (weight ratio) respectively, and then their degradability was investigated under controlled compost and soil burial laboratory conditions for 14 and 28 days. The grades of different composite ratios of PLA films formed were more flexible than pure PLA film. The degradation was measured throughout the period of the experiment by visual inspection, gel permeation chromatography (GPC), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), titration and gas chromatography (GC) analysis were performed on these biopolymer composites before and after degradation experiments. GPC analysis confirmed that the molecular weight of PLA decreased due to degradation, while TGA analysis showed a lower thermal stability for the composites containing more starch. The visual inspection and SEM analysis revealed that the size of polymer composites reduced while the shape became less regular owing to the biodegradation. FTIR spectra of polymer composites showed strong carbonyl bands between 1750.9 cm-1-1760.2 cm-1 that became broader with a slight shift to higher wave number to 1756.1 cm-1-1763.7 cm-1 after degradation. Moreover, the addition of lipase into the compost and soil promoted the degradation rate of polymer composites, leading to the generation of more co2 gas and more weight loss, compared to the experimental results obtained without the use of lipase. To conclude, the degradation rate of PLA/ starch composites can be tailored by changing the composition and environmental conditions (such as temperature and the addition of enzymes).