AbstractFish and seafood may represent risks for human health since they are often contaminated by toxic elementts from aquatic environment, the magnitudes of which are magnified through the food chain. The purpose of this study was to analyze and evaluate the levels of toxic and trace metals in five species of fresh water fish and five species of marine fish bought from commercial markets in Bangkok, Thailand. The edible part of fish samples were analyzed by instrumental neutron activation analysis using the comparator techniques at Thai Research Reactor (TRR-1/M1) at the Thailand Institute of Nuclear Technology. The contents of As, Cd, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se and Zn found in fish samples were 0.19-11.65, <13, 0.10-0.14, 5.34-11.29, <14.00-31.95, <0.55-1.37, <2.00-44.41, <0.30, <0.01, <0.50-2.07 and 18.18-36.92ppm, respectively. As contents in all fresh water fish species did not exceed the standard limit of 2ppm recommended by the Ministry of Public Health of Thailand, but the limit was exceeded in four marine fish species (3.11-11.65ppm). The standard limit recommended for Hg is 0.50ppm, and the amount of Hg in two fresh water fish species and three marine fish species exceeded this limit (0.75-1.37ppm). Cd contents of all fish samples were below the detection limit of 13ppm. While other trace elements are non-toxic.