The severity and duration of immunosuppression caused by corticosteroids (CSs) usage have not been extensively studied. We aimed to investigate the effects of CSs on the various compartments of immune system in relation to timing of initiation and persistence of therapy. Pediatric patients with idiopathic nephrotic syndrome (NS) treated with 2 mg/kg/day prednisolone and healthy control (HC) were enrolled. Blood samples were drawn for immunologic analyses at baseline and at the first and second weeks and first, second, and third months of CS therapy in addition to first and second weeks and first, second, and third months of discontinuation. Fourteen patients (M/F, 7/7) between 1 and 8 years old were evaluated. Untreated NS exhibited high absolute lymphocyte count (ALC)(p = 0.010), absolute CD3(+) T cells (p = 0.020) and absolute CD8(+) T cells (p = 0.006) compared to HC. Suppression in ALC was observed and nadir value was noted at first month of therapy compared to baseline (p = 0.002). The CD4(+) (p = 0.036) and CD8(+) T cell (p = 0.013) counts decreased significantly at the first week of treatment compared to baseline. While baseline B cell counts was indifferent from HC, gradually increased in 2 weeks of CS initiation and decreased during the treatment with a statistical significance compared to HC (p = 0.010). However, after cessation of CS, B cell counts continued to decline and found to be significantly different than baseline at first week (p = 0.008) and at third month (p = 0.040).