The calcium contents of 21 species of fish and nine species of marine invertebrate muscles were determined by atomic absorption spectroscopy. The results are summarized as follows: The calcium contents in fish ordinary muscles and invertebrate muscles were 2.2-39.0 and 5.9-45.5 mg/100 g, respectively. The contents in white muscles were higher than those in reddish muscles. The calcium contents in muscles of small-sized fishes were higher than those in the muscles of lager-sized fishes. The contents of water soluble fraction were higher than those of water insoluble fraction except in common mackerel, skipjack, albacore and blue shark. In fish muscle containing high-level calcium, a high Ca2+-binding protein content was found in water soluble fraction. However, these correlations were not observed in marine invertebrate muscles.