In recent years, anthracnose disease of citrus has caused and contiunes to cause heavy losses to some citrus commercial tree varieties in Mazandaran Province. This disease is deeply spread out in the citrus orchards of the province. In order to isolate and identify the causal agent or agents of the disease, random sampling was done from infected trees during 2004-2005. In lab, samples were cultured on PDA medium. From among 119 samples cultured, 96 Colletotrichum isolates were isolated. Based upon morphological and some physiological characteristics as well as on growth optimal temperature, all the isolates were identified as Colletotrichum gloeosporioides. Pathogenicity severity tests with selected isolates were done on detached branches and as well on two-year old Valencia orange (Citrus sinensis (L.) Osbeck), Unshio mandarin (Citrus unshio Marcow) scions in laboratory and in greenhouse, respectively. The results showed that all isolates were pathogenic on two original cultivars. There were significant virulencedifferences observed (at ? = %1) among the isolates. On the basis of virulence, the lab Valencia and Unshios were respectively divided inot 17 and 15 groups, wherease the greenhouse ones (Valencia and Unshios) divided into 7 and 8 (groups) respectively.