Dicranidae (haplolepideous mosses) are the second-largest group of mosses with about 4000 species, and thus the radiation of Dicranidae is considered to be a major event in the evolutionary process of mosses. However, the present fossil record of Dicranidae is rather limited for understanding the early diversification of this successful and speciose lineage. Here, we describe three new exquisitely preserved haplolepideous mosses as Calymperites heinrichsianus, Calymperites marginatus and Calymperites striatus based on 32 whole gametophytes and 10 gametophyte fragments embedded in 16 pieces of Kachin amber from the mid-Cretaceous of northern Myanmar. The three fossil species all exhibit a combination of characters, including lanceolate leaves with a simple costa, clasping leaf bases with large rectangular hyaline cells (cancellinae), and subquadrate to short rectangular, smooth to slightly bulging upper lamina cells. These characters are indicative of Calymperaceae, a monophyletic family that is placed in the core Dicranales. Considering the mid-Cretaceous age and morphological differences to extant species, the present three species of Calymperites probably represent stem group members of Calymperaceae. They, along with previously reported three species of Calymperites (Calymperaceae) and Ditrichites aristatus (Ditrichaceae or Dicranaceae), provide palaeobotanical evidence for the early diversification of Dicranidae in the mid-Cretaceous Kachin amber forest of northern Myanmar. Palaeoecological habitat reconstruction indicates that Calymperites from Kachin amber has obviously ecological niche differentiation.