Abstract: In order to develop green bast fiber reinforced resin composites with low carbon, energy saving and excellent mechanical and thermal properties and widen their applications, a new kind of modified jute fiber reinforced polypropylene composites (modified JF/PP) with fiber content in range of 10wt%-25wt% was fabricated by a hybrid technique of mill mixing and injection molding process, in which the jute fiber was modified with amino silicone oil invented by our research group in the present work. The effects of modified bast fiber content on the mechanical properties, crystallization behavior, heat resistance (heat deflection temperature) and thermal dimensional stability (linear expansion coefficient) of JF/PP composites were systematically and comprehensively studied. The compatibility and interfacial bonding strength in between the modified and non-modified fiber and PP matrix were analyzed by contact angle test and SEM images. The results indicate that the tensile and flexural strength of JF/PP composites increase with the increase of modified jute fiber content, while the impact strength decreases because the interfacial adhesion between jute fiber and polypropylene matrix is enhanced by modifying jute fiber with amino silicone oil. It is also found from the analyses of DSC, heat deflection temperature and linear expansion coefficient that the addition of modified JF can promote the heterogeneous nucleation of PP and hindered the mobility of PP molecular chain, which lead to the enhancement of the heat resistance property of modified JF/PP composites. The higher the fiber content, the higher heat resistance property of the modified JF/PP will be. When the content of modified JF is 25wt%, the heat deflection temperature of the modified JF/PP is 142.5 ℃, which is 53.5% higher than that of pure PP. Meanwhile, the linear expansion coefficient (CLE) of the modified JF/PP composites decrease significantly with the increase of fiber addition, which suggests that the fiber addition can significantly improve the thermal dimensional stability of the modified JF/PP composites. The linear expansion coefficients of pure PP and the modified JF/PP composites present anisotropic feature. Compared with pure PP, when the fiber addition is 25wt%, the linear expansion coefficientsof the composites decrease by 73.2% in the parallel flow direction and 14.4% in the vertical flow direction. The better mechanical and thermal properties of the modified JF/PP composites will achieve when the fiber addition is in range of 15wt%-20wt%.