Polyhydroxybutyrate (PHB) belongs to the family of polyhydroxyalkanoates and is both, biobased and biodegradable. Due to the linear chain structure, PHB is highly crystalline and the melting temperature is close to the decomposition temperature. Pure PHB crystallizes very slowly, so that the use for some technical applications is not commercially viable. In this paper, the crystallization kinetics of pure PHB and PHB with a nucleating agent is described by means of the differential scanning calorimetry (DSC). The cooling curve and the metabolic rate as a function of the temperature are elaborated. By using a modified Gaussian function, the progression is determined by calculation.