Background: Prescription, a therapeutic transaction between physicians and patient, must be error free, legible and contains all the information to facilitate the dispensing process. However, most of the prescriptions written and arrived at dispensing units are incomplete making the dispensing activity more complicated. Objective: To assess prescribers’ adherence to the basic principles of standard prescription order writing in the different pharmacy units of Mizan Tepi University Teaching Hospital (MTUTH), Ethiopia. Methods: A descriptive cross sectional study was conducted in MTUTH from 5-24, March 2016. Data was extracted from prescription papers using structured data collection format. Three hundred ninety six prescription papers were selected using systematic random sampling method from prescription papers collected over one year period. The data was filled in well-structured checklist and analyzed using SPSS windows version 20 for frequency distribution. Results: Of 396 prescription papers analyzed, only 11(2.7%) prescription papers contained complete patient information. On the other hand, 345(87.1%), 142(35.9%), 357(90.2%), and 272(68.7%) prescription papers contained strength, dose, frequency of administration of drugs and duration of treatment, respectively. Only 17(4.3%) prescription papers contained complete dosage regimen recommendations. Complete prescribers information was found in 268(69.8%) prescription papers. Generally, none of the prescriptions papers complete; i.e., at least one variable was missing. Conclusions: The study revealed a good adherence of prescribers on the basic principles of prescription order writing for some variables and poor adherence for other variables. In order to minimize the therapeutic errors, prescribers should adhere to these principles and hence write all the necessary information required to make prescription papers valid for dispensing. Dispensers on their behalf should not dispense prescription papers with incomplete information. Large scale future studies are important on the area.