Biodiversity is important in human performance and interference in natural environments. Investigation on biodiversity in main forest communities makes the improved management of these valuable ecosystems possible. The aim of this research was the comparison of biodiversity in four major forest communities in Hyrcanian forests.  The four forest communities (i.e., Fagetum, Fageto-Carpinetum, Querco-Carpinetum, Parrotio-Carpinetum) were surveyed by full-callipering method in Patum District of Kheirood forest. Applying the collected data, the biodiversity of them were studied in three levels of trees, shrubs and seedlings. Biodiversity was studied among the mentioned three levels in each association and among the communities separately. The results showed that there was no significant difference among the applied indices (Simpson, Shannon-Wiener and Brillouin) in the study area. Also Shannon-Wiener index decreased in order from Querco-Carpinetum to Parrotio-Carpinetum, Fageto-Carpinetum and Fagetum. There was no significant difference among the associations in the biodiversity of shrubs. The diversity of shrub species in the study area is also independent of the diversity of tree species and seedlings. The study of Shannon-Wiener index showed that the studied communities are different from each other in terms of species diversity, which should be considered in the development of management strategies. Finally, it should be noted that in sustainable forest management should be sought to preserve the diversity of plant species and prevent its decline.