The present study was examined the effects of Bojungchiseup-tang water extract on the renal expression of renal function regulatory proteins including aquaporin 2 (AQP 2), aquaporin 3 (AQP 3), Na, K-ATPase α1 subunit, endothelial nitric oxide synthase (ecNOS), and inducible nitric oxide synthase (iNOS) in rats. The renal expression of AQP 3 was attenuated in rats administered with Bojungchiseup-tang water extract without altered expression of AQP 2, while ecNOS was up-regualted. Oral administration of Bojungchiseup-tang water extract (40 ㎕/100 g) also attenuated the renal expression of Na, K-ATPase α1-subunit and iNOS protein. These results suggest that the diuretic and natriuretic effects of Bojungchiseup-tang maybe causely related with a decreased expression of AQP 3 and increased expression of ecNOS.