Hydroxypropyltrimethyl ammonium chloride chitosan (HACC) is a water-soluble derivative of chitosan. To investigate the immunostimulatory effects of HACC， quaternized chitosans with different molecular weights were prepared and their effects on RAW 264.7 macrophages were compared. The results showed that HACC promoted nitric oxide (NO) production in a molecular weight- and dose-dependent manner. Lower molecular weight HACC was more active in promoting NO production. Furthermore， flow cytometry analysis showed that HACC significantly promoted the production of interleukin-6 and tumor necrosis factor-α. These results were further demonstrated by quantitive real-time reverse transcription polymerase chain reaction and western blot analysis. Moreover， western blotting revealed that HACC induced the phosphorylation of extracellular signal-regulated kinase， c-Jun N-terminal kinase， p38， and signal transducer and activator of transcription (STAT) proteins. In conclusion， HACC activated RAW 264.7 cells through the mitogen-activated protein kinases and Janus kinase/STAT pathways.