Objective: To clarify the epidemiological aspects of visceral leishmaniasis in Kaleybar and Khoda-Afarin districts, north-west of Iran. Methods: A total of 1 420 human (children under 12 years) samples, 101 domestic dogs samples (Canis familiaris), and 577 female sand fly samples were collected. Sera of human and dogs were tested using the direct agglutination test, and sand flies were identified at species level using the microscopic method. Furthermore, a structured questionnaire was applied to evaluate the correlation between the potential risk factors and the related clinical signs/ symptoms with the human and dogs' seropositivity. Results: Totally, 2.18% of human samples were positive at titers≥: 800; among them, 13 cases (41.94%) were above 1:3 200, and clinical symptoms were observed in all of them except for an 11-year old girl. Anti-Leishmania infantum antibodies were found at titers ≥1: 320 in 9.90% of dogs' samples, half of them had at least one sign of canine visceral leishmaniasis. Moreover, 10 Phlebotomus species were identified in the study areas, and Phlebotomus (Larroussius) major group was the predominant species. There are significant correlations between the presence of anti-Leishmania infantum antibodies and the fever (P<0.001), anemia (P=0.001) and weight loss (P=0.016) in children. On the other hand, significant correlations were revealed between the Leishmania infection and the shelter (P=0.039), cutaneous lesion (P=0.005), lymphadenopathy (P=0.001) and weight loss (P<0.001) in the infected dogs. Conclusions: Visceral Leishmania infection is prevalent in rural areas of Kaleybar and Khoda- Afar districts located in East-Azerbaijan province, therefore active detection and treatment of visceral leishmaniasis cases should not be neglected.