The present invention relates to a series of carbazole derivatives which are used in organic electroluminescent devices as the phosphorescent host materials of the emissive layers. The carbazole derivatives have glass transition temperature of between 70.degree. C. and 220.degree. C. and triplet energy of 2.62 eV or more. The carbazole derivatives comprise two carbazole groups and alkyl group and/or spiro group inserted between the carbazole group and aromatic group, which is represented by formula 1. The carbazole derivatives according to the present invention are used as host materials for the triplet emissive dyes and they have high energy and stability. They can also reduce the converse energy transfer from the dye molecules to the host molecules and improve the luminance and efficiency of the OLEDs, especially the efficiency and lifetime of the blue triplet OLEDs. ##STR00001##