Abstract: We analyzed the formaldehyde (FA) concentration in the head, mantle and viscera of purpleback flying squid (Sthenoteuthis oualaniensis) from the central and southern South China Sea. Results show that the viscera had the highest concentration of endogenous FA (average: 93.21 mg · kg^-1); the head and mantle had similar concentrations of FA, with an average of 29.63 mg · kg^-1and 25.69 mg · kg^-1, respectively. Significant difference was not found among the squids of various mantle lengths and those caught from different capturing areas (P > 0.05). However, the FA concentrations in the mantle of squids captured in spring and summer (25.82 mg · kg^-1 and 23.26 mg · kg^-1)and viscera (69.43 mg · kg^-1 and 123.74 mg · kg^-1) were higher than those captured in autumn (5.13 mg · kg^-1 in mantle, 18.15 mg · kg^-1 in viscera, P < 0.05). Compared with other species of the cephalopods family, the purpleback flying squid had relatively lower FA concentration in the viscera, but higher in the mantle(25.69 mg · kg^-1), higher than free FA and free and reversible bound FA (1.09~27.06 mg · kg^-1) in mantles of other types of squid. According to the maximum daily dose reference of 0.2 mg · kg^-1 of FA suggested by US Environmental Protection Agency, the maximum daily consumption of S.oualaniensis for a man of 60 kg is 467 g. The relatively high FA concentration should be attached great importance to during further processing.