This study discussed the effects of jute fiber content and hot water immersion on the tensile properties of jute fiber reinforced polypropylene (PP) composites. The jute/PP composite with different fiber contents was molded by injection molding by dry-blending of jute/PP and neat PP pellets in various mix ratios. Firstly, the quasi-static tensile test was performed. Then the specimens were aged in hot distilled water at 80 A degrees C. After the fixed periods of aging, the changed weight and the tensile properties were investigated. It is found that with the increase of the jute fiber content, the tensile modulus is increased lineally. However, referring to the tensile strength, it is increased firstly followed by a decreased when the jute weight percent is over 30. Additionally, it is found that the weight gain by water absorption was significantly affected by the fiber content. The specimens with the jute fiber content of or over 30 wt% absorbed water easily and significant material loss by aging was also occurred. The tensile strength after aging decreased remarkably in these specimens with the jute fiber content of or over 30 wt%, and all the jute/PP composites showed the lower strength than neat PP after the aging of 1000 h. It is considered that the hydrophilic property of natural fiber decreases the resistance of the composite in humidity environment.