ZnDTP is used in lubricating oils as an antioxidant to inhibit oxidation. However, the use of ZnDTP has been discouraged because it contains phosphorus, which has a high environmental burden, and a new multifunctional additive is required. Thus, fullerenes are attracting attention as a new multifunctional additive to replace ZnDTP. If fullerene-added oils are used in actual equipment, it is essential to have an indicator to detect consumption. However, there is no established method for diagnosing the consumption of fullerenes in lubricating oils. Our present work is to develop a degradation diagnostic method for fullerene-added oils, which are expected to be used in the future. We oxidized the fullerene-added oils and investigated the relationship between the UV absorbance characteristics and the color change of the membrane patch. As a result, the UV absorption spectrum decreased, and the color of the membrane patch changed by scavenging radicals. These consequences indicate that the double bond of the fullerenes is cleaved during the radical scavenging and the resulting fullerene reactants are trapped in the membrane filter. Thus, it is suggested that the consumption of fullerenes can be easily detected by observing the change in hue.