Aims: The present study was aimed to determine whether there exists an altered regulation of aquaporin (AQP) water channels in hypertension. Methods: Male spontaneously hypertensive rats (SHR) aged 10–12 weeks were used. Age-matched Wistar-Kyoto (WKY) rats served as control. The abundance of AQP1–4 proteins in the kidney was determined by Western blot analysis. The protein expression and activity of adenylyl cyclase were also determined. Results: The medullary expression of AQP2 and AQP3 proteins was increased in SHR compared with that in WKY rats. The expression of AQP1 protein was also significantly increased in the inner medulla, while that of AQP4 was not. Immunohistochemistry of AQP2 revealed that principal cells of the collecting duct have strong immunoreactivity, the degree of which was augmented with prominent apical labeling in SHR. The plasma level of arginine vasopressin (AVP) was higher in SHR; the adenylyl cyclase activity stimulated by AVP was augmented, along with increased expression of type VI adenylyl cyclase. The urine was more concentrated with its volume decreased in SHR. Conclusion: The expression of AQP1–3 channels is increased in the kidney, in association with enhanced activity of the AVP/cAMP pathway, in SHR.