Chitooligosaccharides (COS)， the hydrolyzed products of chitin and chitosan， can be obtained by various methods. In this study， water-soluble COS were prepared from α- and β-chitosan by microwave-assisted degradation and their immunostimulatory effects were investigated in RAW 264.7 macrophages. The results indicated that α-COS were more active than β-COS in promoting the production of nitric oxide (NO) and cytokines， such as tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6). Quantitative real-time reverse transcription polymerase chain reaction and Western blotting indicated that COS also enhanced the expression of inducible nitric oxide synthase (iNOS)， cyclooxygenase-2 (COX-2)， and TNF-α. Further analyses demonstrated that COS induced the phosphorylation of extracellular signal-regulated kinase (ERK)， c-Jun N-terminal kinase (JNK)， p38， p85 and Akt， and the nuclear translocation of p65， indicating that they are able to activate the mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinases (PI3K)/Akt signaling pathways dependent on nuclear factor (NF)-κB activation. In conclusion， COS activate RAW 264.7 cells via the MAPK and PI3K/Akt signaling pathways and are potential novel immune potentiators.