Nuclear magnetic resonance (NMR) was used to evaluate the oxidative deterioration of oil in salted dried fish. The ratios of olefinic proteons (Ro) and divinylmethylene protons (Rm) to aliphatic protons in the oil of salted dried fish, as determined by NMR, decreased steadily during storage. On comparing Ro and Rm with data for peroxide value (PV) and acid value, Ro was shown to serve as an index of the oxidative deterioration of the oil of salted dried fish, particularly in the case of oil whose PV had decreased.