A category of polyethylene glycol-polyurethane (PU) foams were prepared by chitosan (CS) with different molecular weight as chain extender. The activity group, CS grafting degree, crystallization behavior, morphology, thermal stability, mechanical properties, hydrophilicity, protein adsorption and degradation in vitro of PU-CS composite foams were investigated. The experimental results indicated that better group reactivity (-NH2 and -OH) in CS with low molecular weight led to the higher CS grafting degree (78.9% and 98.3%) in the PU foams modified by aminoglucose (CA) and chito-oligosaccharide in 3000 g/mol (CS3K). The disordered crystallization behavior of PU-CA composite foams appeared due to both -NH2 and C6-OH in CA with high activity. However, a clear crystallization diffuse peak in PU-CS3K similar to that in pure PU was presented because the activity of -NH2 in CS3K was relatively high. The phase separation and disorder bubble holes appeared in PU-CS composite foam when CS with high molecular weight in 30,000 g/mol and 300,000 g/mol (CS30K and CS300K) were used. It was the high grafting degree of CS that PU-CS3K had relatively high thermal stability. With the increase of CS molecular weight, the tensile strength, the hydrophobicity, the protein adsorption and the degradation rate of PU-CS composite foam increased. Although pure PU and PU-CS composite foam with low molecular weight of CS (CA and CS3K) have similar hydrophilicity, the adsorption amount of BSA on the latter increases obviously owing to the electrostatic adsorption of amino groups, and the degradation rate of latter during the early stage of degradation is lower than that of former due to the relatively large number of chemical crosslinking sites. These experimental results presented new suggestions for the research and application of CS in PU based biomaterials.