Organotins, especially tributyltin (TBT) and triphenyltin (TPT), are of particular concern due to their ubiquity in the aquatic environment and theirtoxicityto aquatic organisms. This study reports field studies on trophic magnification factors (TMF) of TBT and TPT in a marine food web. TBT, TPT, and their metabolites in plankton, five benthic invertebrate species, and six fish species collected from Bohai Bay, North China were determined, and it was found that the concentrations of TPT in marine fish were unexpectedly higherthan those of TBT. A positive relationship was found between trophic levels and concentrations of TPT, indicating trophic magnification of TPT in this food web. The TMF of TPT was calculated to be 3.70. On the other hand, concentrations of TBT, dibutyltin (DBT) and monobutyltin (MBT) did not exhibit statistically significant trends with trophic levels, and the TMF of TBT was 0.59. Analysis of organotins in the water and surface sediment from Bohai Bay revealed low inputs of TPT to the environment, which indicated that the high concentrations of TPT found in fish from Bohai Bay were due to the food web magnification of TPT.