The present study aimed to investigate changes in the mammalian target of rapamycin (mTOR) signaling pathway in the obstructed kidney of rats with unilateral ureteral obstruction (UUO). Male Sprague-Dawley rats were unilaterally obstructed by ligation of the left proximal ureter for 7 days. Control rats were treated in the same way except that no ligature was made. The expression levels of phosphorylated phosphatidylinositol 3-kinase (PI3K), Akt, and mTOR were determined in the kidney by semiquantitative immunoblotting. The protein expression levels of transforming growth factor (TGF)-β1, Bax, and Bcl-2 were also determined in the kidney. The phosphorylation of PI3K, Akt, and mTOR was increased in the kidney of ureteral obstruction rats compared with the control. In the obstructed kidney, the protein expression of TGF-β1 and Bax was also increased, whereas Bcl-2 expression was decreased. In conclusion, the phosphorylation of PI3K/Akt/mTOR was increased in the obstructed kidney of rats with UUO.