To provide an incombustible filter medium for an ultraviolet-resistant air-conditioning filter realizing a high particle collection efficiency with a low pressure drop, having gradual pressure drop increase due to dust clogging, and to provide a sock filter composed of the filter medium.

This filter medium for the ultraviolet-resistant air-conditioning filter is composed of a filter medium containing triboelectric charging nonwoven fabric. The triboelectric charging nonwoven fabric comprises at least 20 mass% polyester-based fiber containing phosphinic compound and/or sulfonic compound, and at least 30 mass% polyolefin fiber. The sock filter is composed of the filter medium.