It is predicted in 2019, 91.1% of capsule shells produced are made from gelatin which is not suitable for vegetarians and some religious groups. Research on vegetable capsule shells began to develop to substitute gelatin using seaweed extracts such as carrageenan, alginate, HPMC, and polyhydroxybutyrate. Spirulina platensis microalgae is a PHB producer that is easy to cultivate, and its production can be optimised by modifying the extraction method. Solvent extraction is the most simple and economical extraction method with general stages in the form of cell disruption, PHB precipitation, and PHB purification. Sodium hypochlorite (NaClO) is a cell-disrupting solvent that is widely used for the extraction of PHB from microalgae. The parameters tested in this study consist of concentration of S. platensis sample cells shown as optical density (OD) ranging from 1, 2, 3, 4, 5, and 6. The PHB quantification and characterization method used was FTIR, and it showed the similarity between extracted PHB from Spirulina platensis with commercial PHB. The expected results of this PHB extraction are to get the maximum yield of PHB and the most efficient extraction method based on the independent variables. Extraction of microalgae sample with OD 4 using 4% NaClO is expected to have the highest yield of PHB.