A new species, Cimbrophlebia rara sp. nov., in the family Cimbrophlebiidae (Mecoptera) is described and illustrated. This specimen was collected from the Early Cretaceous Yixian Formation at Liutiaogou in Inner Mongolia, China. This is the first record of a cimbrophlebiid from the Jehol biota. A key to all species of Cimbrophlebia is given. A preliminary review of published taxa data indicates that from the Middle Jurassic to the Early Cretaceous, Mecoptera became less diverse and less abundant in northeastern China at familiar level (from 11 to 6), generic level (from 32 to 8) and specific level (from 44 to 14).