Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] is a biodegradable polyester from the family of polyhydroxyalkanoates. In the first part of this study, the thermal influence on the molecular mass and isothermal crystallization kinetics of P(3HB-co-3HHx) were investigated. The molecular mass decreases with increasing isothermal holding temperature and time. Avrami model has been successfully used to describe the isothermal crystallization kinetics of P(3HB-co-3HHx). Following the initial outcome, P(3HB-co-3HHx) was blended with epoxidized natural rubber (ENR). The blend is expected to yield polymers with combination mechanical or thermal properties. It is shown that ENR promotes the isothermal crystallization rate of P(3HBco-3HHx) despite forming immiscible constituents with P(3HB-co-3HHx). The thermal property of P(3HB-co-3HHx) is influenced by the presence of ENR after isothermal crystallization. Further experimental result shows that the P(3HB-co-3HHx) and ENR can be reacted in-situ using differential scanning calorimeter. The kinetic of melt reaction shows good approximation and similar behavior to that of other melt reaction systems such as poly(3-hydroxybutyrate)/ENR and poly (3-hydroxybutyrate-co-3- hydroxyvalerate)/ENR blends
