Visceral leishmaniasis (VL) or kala-azar is a parasitic disease caused by Leishmania donovani complex. Evidence suggests that visceral leishmaniasis is prevalent in some areas of Mazandaran and Golestan provinces. This study aimed to investigate the cases and also determining the causative agents of VL in these provinces. In this study, seven VL patients (mean age 1.5 years) admitted to the pediatric departments in Sari Booali Sina and Gorgan Taleghani hospitals, 2013–2016, were examined. The most common clinical and laboratory findings included prolonged fever, hepatosplenomegaly, anemia, pancytopenia, and hypergammaglobulinemia. Blood and bone marrow (B.M) samples were taken. Direct agglutination test (DAT) and rapid rK39 strip test were used as serologic tests and B.M microscopic slides were checked by species-specific PCR to identify the parasite species. All patients had positive rK39 and DAT tests. Examination of bone marrow smears demonstrated amastigotes of Leishmania (Leishman bodies) in the samples. The species of Leishmania in all B.M smears was Leishmania infantum. According to the identification of L. infantum as the major agent of VL in Mazandaran and Golestan provinces, increasing physician awareness (especially pediatric specialists) of the disease and conducting control programs in these areas are recommended.