This study describes two cases of urolithiasis-related mortality in Asian small-clawed otters (Aonyx cinerea) raised together for over 10 years. Case 1 had multiple renal and bladder stones without clinical signs and died during surgery for stone removal. Case 2, which harbored more extensive renal calculi, also showed no clinical signs but died suddenly from hydronephrosis and renal failure caused by bilateral obstruction of the renal pelvis. In both cases, the uroliths were composed of calcium oxalate. These results highlight the importance of regular examinations in captive otters.