We investigated the effects of melatonin (Mlt) on hematological characteristics to determine the percentage of alpha-naphthyl acetate esterase (ANAE) positive lymphocytes in rats chronically exposed to cadmium (Cd). We used four groups of male rats: control (C), melatonin (Mlt), cadmium (Cd) and Cd + Mlt (CdMlt). Blood samples were obtained to assess the erythrocytes (RBC), leukocytes (WBC), platelets (PLT), hemoglobin (HGB), hematocrit (HCT), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV) as well as alpha-naphthyl acetate esterase (ANAE) positive lymphocytes. We found that the number of WBC increased in the Cd group compared to the other three experimental groups. Low MCV and MCHC values caused by Cd were ameliorated by Mlt treatment in the CdMlt group. We found no significant change in the RBC, HGB, MCH, PLT and HCT values among the experimental groups. Mlt treatment also increased the percentage of ANAE positive lymphocytes. Mlt partially protects some hematological characteristics in cases of chronic Cd toxicity.