Mercury is one of the heavy metals which rapidly accumulated into fish muscles. Accumulated mercury in the body of fish came from a polluted environment and their prey. Consuming fish infected with high-concentrated mercury could endanger human health. The purpose of this study was to observe the concentration of mercury in Yellowfin Tuna and Indian Mackerel samples from Bitung Fish Auction Market, North Sulawesi. Samples were divided into two categories, fillet and frozen fillet for Yellowfin Tuna’s samples, fillet and whole fish for Indian Mackerel’s samples. Mercury in samples was analyzed in Toxicology Laboratorium at Research Centre for Oceanography Indonesian Institute of Sciences (RCO-IIS) using Mercury Analyzer model MA-3000. The results showed that mercury concentrations in Yellowfin Tuna’s samples were 67.54 μg/kg and 737.84 μg/kg for fillet and frozen fillet, respectively. Meanwhile, mercury concentrations in Indian Mackerel fillet and whole fish samples were 146.35 μg/kg and 38.35 μg/kg, respectively. The mercury concentrations in the samples complied with SNI 7387-2009 and BPOM No. 23 – 2017 mercury standards.