Abstract: OBJECTIVE To evaluate the effects of pharmaceutical intervention on medication complexity and safety for elderly hospital inpatients. METHODS A before-after intervention study involving patients aged 65 years and over was carried out. Clinical pharmacists participated in the programs of pharmaceutical intervention and made recommendations to hospital medical officers to simplify regimens in the intervention group. Medication regimen complexity(MRC) and potentially inappropriate medicines(PIMs) was measured by the medication regimen complexity index(MRCI) and Beers Criteria 2015 between admission and discharge for regularly scheduled long-term medications respectively. Then the MRCI score, the proportion of PIMs, and the incidence rate of adverse drug events(ADEs) were observed in both phases and the medication compliance, and the satisfaction were compared. RESULTS The MRCI score at discharge was significantly higher than at admission in the no-intervention group and the intervention group(P<0.01 or P<0.05), but the mean increase in MRCI score between admission and discharge was significantly smaller in the intervention patients than in the no-intervention patients(5.4±5.9) points vs (2.3±5.6) points, P<0.01. Compared with the no-intervention group, the proportion of patients prescribed at least one PIMs decreased significantly, from 57.0% to 42.9% at discharge between two groups(P<0.01). After pharmaceutical intervention, the drug adherence outstanding rate and pharmacy service satisfaction were significantly better than those in the no-intervention group, whereas the incidence rate of ADEs was quite lower(P<0.01). However, there was no significant difference in the average hospitalization time between the two groups. CONCLUSION A pharmaceutical intervention with medication regimen simplification can not only reduce the impact of hospitalisation on MRC and the proportion of PIMs, but also improve the safety, economy and rationality of drug use in elderly patients.