Abstract: Visceral leishmaniasis is one of the most important health problems in Iran which is transmitted by sandflies species to human. In order to determine vector/s of the disease an investigation was carried out in Meshkinshahr district, the most important focus of the disease in Ardebil province, north west of Iran, during 2001-2005. Using sticky papers, CDC light traps and aspirators, totally 2500 sandflies were collected and identified at the species level. Host blood preference and natural infection of female specimens to promastigotes were tested, respectively using ELISA and dissection followed by PCR assay using species-specific kinetoplast minicircle primers. Results showed that six species of Phlebotomus kandelakii, P. perfiliewi transcaucasicus, P. papatasi, P. jacusieli, P. caucasicus and P. sergenti were present in the district, where P. kandelakii with 40% was the most prevalent species. Anthropophilic index of P. kandelakii species was calculated 32.8%, indicating a strong preference to human. Among the dissected female sandflies, only 11 out of 1002 (1.1%) of P. kandelakii was found naturally infected with promastigotes. Species-specific amplification of the Giemsa stained promastigote slides revealed specific PCR products of Leishmania infantum DNA in the infected P. kandelakii sand-flies. Having found high prevalence and anthropophic index and natural infection to Leishmania infantum provide enough evidences to incriminate the species of P. kandelakii as the main and proven vector of visceral leishmaniasis for the first time in the region and in science.