Plastic production in Indonesia yearly has surpassed the 4.6 million tons and accumulated in aquatic system. Polyethylene terephthalate (PET) and Polypropylene (PP) are the most widely used plastics in manufacture of packaging, fibres, and drinking bottles, etc. The degradation of these plastics to micro sizes lead to environmental threats especially when the micro plastic interact with fresh water microorganism such as microalgae. Therefore, the study of interaction between micro plastic and microorganism is really important. The aim of this study is to evaluate the impact of micro plastic to the growth of microalgae Spirulina sp and also to evaluate the contribution of microalgae Spirulina sp to the plastic degradations. The interaction between microalgae and microplastic was evaluated at a 1 L glass bioreactor contained microalgae Spirulina sp and micro plastic PP and PET with the size of 1 mm at various concentration (150 mg/500 mL, 250/500 mL and 275 mg/500 mL) for 112 days. The results showed that the tensile strength of micro plastic PET decreased by 0.9939 MPa/day while PP decreased by 0.1977 MPa/day. The EDX analysis of micro plastic showed that the decreasing carbon in PET (48.61%) was higher as compared to PP (36.7%). FTIR analysis of Spirulina sp cells showed that CO2 evolution of cells imposed by PET micro plastic was higher than imposed by micro plastic PP. The growth rate of Spirulina sp applied by micro plastic was lower than the control and the increase of micro plastic concentration significantly reduced the growth rate of algae by 75%. This research concluded that biodegradation has important role in degradation process of plastic