Sirvan watershed area with ??7,500 km ², is one of the Iran and Kurdistan basins with highest rainfall, whereas 2.8 billion cubic meter surface water in the basin is running in Kurdistan province. Sirvan River originates from Asadabad (Hamedan province) and Sonqor (Kermanshah province) and join, Qeshlaq, Marivan and Gavrud, where it is named Sirvan River and finally pours into the Tigris and the Persian Gulf. Sirvan basin fish species diversity in spring and summer was studied. Twelve stations were selected based on structural differences (length, width, depth and flow intensity of river), tributaries joining points and level of human interferences (dams, reservoirs and land mining). The sampling was conducted using different capturing and fisheries gears (different nets). Captured specimen were fixed in 10% formalin, then traorted to laboratory and preserved in 70% ethanol. For identifications, some meristic traits like scales number (on lateral line, below lateral line and above lateral line) and number of fin rays were counted, the location of fins and oral forms were examined and compared with valid identification keys. Totally 1454 fish specimens were captured and identified amongst which 17 species belonged to Cyprinidae, Salomonidae, Nemachelidiae and Gobiidae. There were significant differences in species frequency and species number at each station, during both seasons of spring and summer. Cyprinidae accounted for 98% of all samples with highest distribution and species number; 97% of identified samples, were native. The least frequency was recorded for Salmonidae family. The Vahdat dam station had the highest specimen frequency and Nosoud one had the highest species number. The least specimen frequency was related to Hajij station and the least number for species was observed in Palangan station. Alburnus mossulensis had the highest frequency and Carassius auratus , Luciobarbus pectoralis and Oncorhynchus mykiss the lowest one. Also, six exotic fish specimens were captured including Ctenopharyngodon idella , Carassius auratus , Rhinogobius similis , Hemiculter leucisculus, Pseudorasbora parva and Oncorhynchus mykiss . For Species richness, Margalef index, for species diversity, Shannon index and for species dominance, Simpson index was used. The number of species increased in the summer, so that the index of species richness between the two seasons was significantly different at various stations. The highest species richness index was in Bolbar station, the highest species diversity index in Vahdat Dam station in summer and the highest species dominance index was in the spring season, in Divzenav station. Most of the aquatic ecosystem disturbant factors were observed e.g., dam construction (Vahdat dam station), river bed disturbance (Nosoud, Qalaji and Vahdat dam stations), introduction of exotic species (Vahdat dam station), reservoir construction (Nezar, Kumaeen, Faghih Solayman, Hajij Stations) and establishment of aquaculture farms (Palangan, Divzenav, Nosoud Stations). Due to the impact of human intervention in this basin, the number of species from upstream to downstream was not in a specific order. Keywords: Cyprinidae, Freshwater fishes, Gobiidae, Nemacheilidae, Salmonidae, Sirvan basin, Species diversity.