Aspirin is widely used for treatment or prophylaxis of many diseases. Although aspirin is used chronically for preventing cardiovascular diseases especially, liver function is rarely monitored because of unpredictable and uncommon hepatotoxicity induced by aspirin. We evaluated changes in liver function indicators and compared to acetaminophen and NSAIDs. We retrospectively analyzed EMR data (n=28788) of patients who took study drugs and had liver function tests (LFT) during study period from 2009.7.1 to 2010.6.30 at a tertiary hospital and evaluated the above information. Patients not having LFT results at these three standard points of time (baseline, during medication, and after finishing medication) were excluded. During medication, mean changes of Alanine transaminase (ALT), Aspartate transaminase (AST), Total Bilirubin (TB) were increased and that of serum albumin (Alb) was decreased, with the largest effect from aspirin (n=461; 16.8, 14.9, 0.28, -0.24) and the smallest from celecoxib (n=127; 3.4, 5.2, 0.11, -0.16). In addition, aspirin caused more changes of blood liver function indicators in patient group with liver disease (n=128, 27.4, 26.9, 0.53, -0.3) than those in patient group without liver disease (n=357, 12.5, 13.1, 0.23, -0.24). Taking low dose aspirin for prophylaxis purpose with long-term medication may be associated with liver injury. Our study is just a signal regarding the possibility of hepatotoxicity among patients taking low dose aspirin in a hospital setting, and thus it needs to be further investigated.