Plastics that are widely used today are still made of synthetic polymers that are difficult to degrade by soil microorganisms. The development of natural polymer such as protein blend with synthetic polymer for bioplastic manufacturing continues. This study will utilize Spirulina platensis blended with synthetic polymers with heating and sonication as pre-treatment to optimize the characteristic. In this research, 2.5 g of Spirulina platensis powder dissolved in alkali and distillate water with pH variation of 7, 8.5, 10, and 11, then plasticized by glycerol and heating at 70oC with heating time variation of 30, 60, and 120 minutes. After that, blending with 2.5 g polyvinyl alcohol. Mixed solution then dried and formed as flex bar. Based on the results of solvent pH variation, the degree of acidity of the best solvent to produce optimum mechanical properties is a solvent with a pH of 10. The best heating time to produce optimum mechanical properties is 60 minutes at a solvent pH above 8.5. If using a solvent pH below 8.5, the best heating time is 120 minutes. Degree of solvent acidity is the most influential parameter on the bioplastic mechanical properties of Spirulina-PVA while the heating time has no significant effect.