Study on biodiversity of springtails (Hexapoda: Collembola) in three different ecosystems in Kermanshah province, Iran.The biodiversity of Collembola were evaluated in three different ecosystems: field crop, oak forest and grassland in two cities (Paveh and Sare pol-e- Zahab) monthly from May 2012 to May 2014. In each site, one soil sample collected with a diameter of 10 cm and 13 cm depth. Species richness, biodiversity and the indices of similarity, were calculated using α , β, γ, Shannon-Wiener, and Jaccard-Sorenson indices. The results showed that the biodiversity and species richness of forest was higher than the field crop and grassland in two different cities. In Paveh, the species richness of field crop was higher than the grassland however, there was no significant difference between field crop and grassland in Sare pol-e- Zahab city, unexpectedly. Comparison between the similar ecosystems among two counties showed that the biodiversity of Paveh's forest was higher than the forest of Sare pol-e- Zahab. In contrast, the biodiversity in Sare pol-e- zahab's grassland was higher than the Paveh and there was no significant difference among field crop in two different cities. Comparison of Shanon- gamma index among the two cities showed that biodiversity of Paveh was higher than the Sare pol-e- Zahab. Comparison of similarity among the different ecosystems showed that field crop and grassland had more similarity compared to forest in two different cities.