In this study, we establish a thin-layer chromatography (TLC) immunostaining method for detecting starfish gangliosides. A new monoclonal antibody (MAb) against AG-2, the major gangliosides molecular species of Acanthaster planci, was produced by fusing hybridoma with splenocytes immunized to liposomal AG-2. BALB/c male mice were injected with liposomal AG-2 antigen, and immunized. Their splenocytos were isolated and fused with hypoxanthine-aminopterine-thimidine (HAT)-sensitive mouse myeloma cells. Hybridomas producing MAb reactive to AG-2 were cloned using the limited dilution method. Established hybridomas were cultured in eRDF medium. Crude MAb produced from clone 8D4 was purified with a magnesium pyrophosphate column. Enzyme immunoassay and TLC immunostaining of AG-2 were performed using the purified MAb. Structurally related gangliosides did not cross-react with anti-AG-2 antibodies. The detection limit of TLC immunostaining was 50 ng of AG-2. The newly established immunostaining method was further developed for detecting AG-2 distribution and qualitative analysis in tissues and/or organs. Our results show that the majority of AG-2 is present in the stomach of male A. planci, while AG-2 is distributed not only in the stomach but also in the the pyloric caeca of female A. planci.