In this research work, the untreated and various concentrations of alkali treated continuous mulberry fibers were used as reinforcement in polyester matrix and its static and dynamic mechanical properties were investigated. The composites were fabricated using untreated, 5%, 10%, and 15% alkali treated mulberry fibers (ATMF) reinforced in polyester resin by compression molding technique. The result showed that the 10% alkali treated mulberry fiber composite (ATMFC) considerable increase in tensile, flexural, and impact properties compared to untreated, 5% and 15% alkali treated mulberry fiber composites. The 15% alkali treated mulberry fiber composite showed decrease in water absorption property. The fractured surface morphology of composite samples was examined by Scanning Electron Microscopy (SEM). The Dynamic Mechanical Analysis (DMA) shows that the 10% alkali treated mulberry fiber composite enhanced storage and loss modulus compared to untreated, 5% and 15% alkali treated mulberry fiber composites. The weight loss of untreated, 5%, 10%, and 15% alkali treated composites were studied under varying temperature by Thermo Gravimetric Analysis (TGA) and Differential Thermo Gravimetric analysis (DTG). POLYM. COMPOS., 39:E1908–E1919, 2018. © 2018 Society of Plastics Engineers