Adsorption and thermal stability of Sm and Gd thin layers on Mo(111) surface was investigated using Auger electron spectroscopy (AES), low electron energy diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoemission spectroscopy and work function change measurements (Δϕ). At 300K the first three layers of Sm grows in the monolayer-by-monolayer mode. Sm forms initially a pseudomorphic layer of trivalent atoms, which is probably completed to a densely packed layer in part by divalent Sm atoms. In contrast, the second Sm monolayer is entirely composed of divalent atoms. Gd also grows in the monolayer-by-monolayer mode in the investigated coverage range. At higher temperatures (800K for Gd and 530K for Sm) only the first layer is thermally stable. Both adsorbates did not cause surface reconstruction or faceting