Objective:To construct chimeric mouse-human Fab antibody from a mouse monoclonal antibody NP11-4 which is specific to membrane protein of Schistosoma japonicum by genetic engineering technique,and further identify the binding ability of chimeric antibody fragment. Methods:Light chain variable region(VL) and heavy chain variable region(VH) genes cloned from mouse monoclonal antibody NP11-4 were amplified by RT-PCR,and sequenced and analyzed after being ligated into pMD18-T vector. Then VH and VL were fused into CH1 domain of human IgG1 and CL domain of human kappa chain respectively to obtain fragments of Fd and light chain. Chimeric Fab(cFab) was amplified by overlap PCR from chimeric genes of Fd and light chain. After the cFab DNA was ligated into the phagmid vector pComb3XSS,the expression vector pComb3XSS-Fab was transformed into E. coli Top 10F’,and the of soluble protein induced by IPTG(isopropyl-β-D-thiogalactoside) was detected. The expressions of products were detected by ELISA and Western blot methods. Results:An expression vector pComb3XSS-Fab to express cFab against Schistosomiasis japonica was successfully constructed. The cFab protein was expressed in soluble form and secreted form,which was confirmed by Western blot. ELISA demonstrated that the cFab possessed the activity and specificity of interacting with SEA(soluble egg antigen). Conclusion:The cFab retained the high affinity and specificity similar with the original mouse mAb NP11-4. This cFab fragment can be further modified to generate immunotoxin for therapeutic uses.