Abstract: Objective：To explore and investigate the effect of clinical pharmacists participating in medical prescription checking and intervention in the rational drug use of chemotherapy patients in thoracic surgery. Methods： Main problems found during clinical pharmacists participating in prescription checking in our hospital from August 2016 to July 2017 were analyzed respectively. Prescription of chemotherapy patients was analyzed statistically in thoracic surgery during April to July in 2016(before intervention)， August to November in 2016（after the first intervention）， December 2016 to March 2017（after the second intervention）and April to July in 2017(after the third intervention）. Results： The irrational types in prescription included unsuitable solvent type and amount， inappropriate drug combination， unsuitable usage and dosage， inappropriate indications， unsuitable drug selection，incompatibility， and inappropriate treatment course，etc.The irrational rate of prescription of patients with chemotherapy was 6.47％ before intervention， and 4.50％，2.70％ and 1.17％ after the first， second and third intervention respectively， the difference was statistically significant compared to before intervention（P＜0.05）. Recommended adoption rate for pharmacists rising in turn after the first， second and third intervention 50.27%， 68.70% and 87.04% respectively， the difference was statistically significant compared to the first intervention（P＜0.05）. Conclusion：Clinical pharmacists participate in medical prescription checking and intervention is propitious to rational drug use.