Medicines wastage occurs when medicines are damaged, obsoleted or expired and becomernunsafe for use. It is a burden to many health facilities and increases cost to the health carernsystem. In Ethiopia, although there are reports that reveal the presence of wasted medicines inrnthe country, there is limited objective evidence on the type and extent of medicines wastage asrnwell as its contributing factors. Therefore, the objective of this study was to determine medicinesrnwastage rate and to identify its contributing factors in the sampled public health facilities ofrnSouth West Shoa Zone, Oromia Regional State, Ethiopia. The study employed a facility basedrncross-sectional survey and qualitative study in one hospital and nine health centers from May 2-rn27, 2016. Both quantitative and qualitative data collection methods were used in the study. Thernquantitative data was collected by data abstraction formats and self-administered questionnairesrnand analyzed using SPSS version 21.0. The analysis was performed in aggregate and includedrndescriptive statistics. And the qualitative data was collected through in-depth interview with thernheads of the health facility and pharmacy case team leaders and analyzed using thematicrnanalysis. The total monetary value of wasted medicines in the surveyed health facilities in EFYrn2005-2007 was 500,522.09 Ethiopian Birr, while in the same period all surveyed health facilitiesrnreceived medicines worth of 6,635,910.97 Ethiopian Birr, resulting wastage rate of 7.5%. Of therntotal value of wasted medicines, anti-infectives (39.1%), medicines used for correcting water,rnelectrolyte and acid-base balance (12.9%) and GIT medicines (10.6%) were the top threerntherapeutic classes. Oral rehydration salt 245osml/l powder (6.3%), metronidazole 250mgrncapsule (4.1%), and tetracycline 250mg capsules (3.2%) were also the most commonly wastedrnmedicines. More than half of the wasted medicines were in solid dosage forms (54.3%), followedrnby liquid dosage forms (40.8%) and nearly 96% of the source for wastage was expiry ofrnmedicines.rnIXrnIn both quantitative and qualitative study, delivery of near expiry date medicines by suppliers,rnlack of system to move nearly expired medicines from one facility to another, presence of overrnstocked medicines due to improper forecasting of need in the facilities, lack of electronic stockrnmanagement tools and shortage of pharmacy professionals in the health facilities were identifiedrnas contributing factors for medicines wastage. In conclusion, the extent of medicines wastage inrnpublic health facilities of South West Shoa Zone was estimated to be 7.5%. It is recommendedrnthat the health facilities should document and maintain a written record of all medicines wastage.rnA mechanism of exchanging medicines from overstock to under stock areas should be created, and arnstrong partnership or a common plat forum should be established among key stake holders tornhave regular discussion on preventive strategies.rnKey words: Medicines wastage, wastage rate, expired medicines, public health facility,rnEthiopia