An effective and sensitive method was developed for simultaneous determination of albendazole and its three metabolites in shrimp and crab using multi-walled carbon nanotubes (MWCNTs) as solid phase extraction (SPE) sorbent coupled with ultra-performance liquid chromatography-tandem mass spectrometry. In the whole procedure, the multi-isotope dilution method was used to correct the loss during the SPE and variations associated with the analysis. Under optimum conditions, the method was validated with respect to linearity, specificity, accuracy and precision. The linearity of the method was good in the rang from 0.1 to 20 ng/mL, with regression coefficients all above 0.9986. The limits of detection and quantification for the four analytes were 0.02-0.04 and 0.06-0.12 ng/mL. The mean recoveries in both matrices spiked at range from 0.2 to 5.0 ng/g were 95.2-104.0%, with intra-day RSDs less than 5.26%, and inter-day RSDs less than 4.25%. The method was later successfully applied to real shrimp and crab samples for the determining and confirming of albendazole and its three metabolites.