The object of the present invention is to provide a deterioration smell inhibitor capable of effectively inhibiting deterioration smell generating form various products such as foods and cosmetics. The present invention relates to a deterioration smell inhibitor comprising a plant extract and isothiocyanate. As preferred embodiments, the plant extract is a labiatae plant extract, further the labiatae plant extract is an oil-insoluble labiatae plant extract, still further the weight ratio of the oil-insoluble labiatae plant extract/isothiocyanate is 1/1 to 99/1. In other preferred embodiments, the plant extract is a terpenoid alcohol or terpenoid ketone, further the weight ratio of the terpenoid alcohol or terpenoid ketone/isothiocyanate is 0.4/1 to 40/1.