The Aim of this research were to investigate the effect of alkaline treatment on the mechanical properties of material bio-composite sansevieiria trifasciata fiber/Polypropylene and to analyze the morphology of interfacial bond between fiber and matrix. In this research, bio-composites sansevieria trifasciata fiber/Polypropylene was manufactured by using a hot press method with temperature 240oC and pressure 140 Bar for 10 minutes. Fibers were extracted from Sansevieria trifasciata by using mechanical retting. In this experiment, the mechanical properties and morphology of alkaline treated fiber and non-alkaline treated fiber was investigated, the fibers were treated by NaOH 3% (w/w) solution at temperature 100oC for an hour. The volume fraction of fiber used in this experiment were 0%, 5%, 10%, and 15% with unidirectional orientation. Actual density and mechanical properties of bio-composite were conducted based on ASTM standard testing methods D792 and D3039. In this research, it found that tensile strength modulus of elasticity and elongations of sansevieria trifasciata/polypropylene bio-composite alkaline treated were higher than that of untreated. The fracture analysis was investigated by scanning electron microscope (SEM). The highest tensile strength and stiffness of biocomposites were 59.77 MPa and 1.98 GPa respectively, obtained from bio-composites with volume fraction of unidirectional alkaline treated fiber 15%. Morphological feature based on scanning electron microscope (SEM) observation showed that alkaline treated fibers had better interface bond compared to non-alkaline treated fibers.