Myoglobin is known to be present exclusively in cardiac and red skeletal muscles, but not in white skeletal muscles. Thus, to date, only a few studies on myoglobin from fish species with white flesh have been reported. For comparative examination, we directly isolated myoglobin from cardiac muscle of hoki (Macruronus magellanicus), one of the most important commercial fish species with white muscle. The ferrous myoglobin was separated from its ferric met-form by anion exchange column chromatography. The absorption spectra of hoki myoglobin were similar to those of bigeye tuna skeletal myoglobin, in both oxy- and met-forms. However, hoki oxymyoglobin was found to be susceptible to autoxidation in 0.1 M buffer (pH 7.2) at 25°C, with its rate being more than 3 times higher than that of bigeye tuna oxymyoglobin.