Polymer composites based on polyamide 11 (PA11) and bamboo flour (BF) were prepared by a melt mixing method on Haake equipment. In order to improve the adhesion between components of the composites, polyvinyl alcohol (PVA) at different concentrations was added into the composites by the two following methods: PVA, PA11, and BF were mixed together in the melting state (abbreviated as the melting method); and BF was treated by PVA in a ethanol solution before added into the composites (the modifying method). The result of tensile test showed that the tensile strength (TS) of composites produced by the modifying method is higher than that of other composites fabricated by the melting method. At the ratio of PA11/BF (60/40) and PVA concentration of 10 wt.%, the TS value reached the highest peak at 41.5 MPa. Besides, the elongation at break of the composites is 6.9%. The composites prepared by the modifying method had lower water uptake for 24 h than that of the melting method. It means that PVA played a more effective role in the modifying method in comparsion with the melting method. The result was also relevant with the observation of the fracture surface of composites by SEM images.