We aimed to assess the effect of aliskiren treatment on blood pressure, albuminuria, and kidney function in patients with chronic kidney disease (CKD). We conducted a prospective, open-label study of 67 patients with CKD who were already being treated with other antihypertensives. Inclusion criteria were blood pressure (BP) ≥130/80 mmHg, albuminuria ≥30 mg/g, and estimated glomerular filtration rate (eGFR) >30 ml/min/1.73 m². Subjects were treated with 150 mg/day aliskiren, which was increased to 300 mg/day for the 24-week study period. Aliskiren effectively reduced both systolic and diastolic BP, plasma renin activity (PRA), serum aldosterone concentration, albuminuria, urinary N-acetyl-glucosaminidase, and urinary β2-microglobulin levels. Although eGFR was significantly decreased after 4 weeks of aliskiren treatment, it recovered to a pretreatment level within 12 weeks of treatment initiation. There were no significant differences in the percent reduction of albuminuria or changes of eGFR levels when the subjects were divided into three groups on the basis of baseline eGFR (stages 1/2, 3, and 4) and the presence or absence of diabetes mellitus (DM group and non-DM group). Furthermore, in patients not treated with renin-angiotensin-aldosterone-system (RAAS) inhibitors, including angiotensin receptor blockers or angiotensin-converting enzyme inhibitors at baseline, changes in eGFR were significantly increased compared with those already treated with RAAS inhibitors at baseline. Aliskiren administration reduced BP, PRA, serum aldosterone levels, and albuminuria, while maintaining eGFR, regardless of the presence or absence of DM or the degree of eGFR.