Studies reported from Ethiopia depict poor health outcomes and management of diabetes cases and low patients" adherence to recommended regimens including medications. Among factors determining adherence to medications that are amenable to interventions are patient perceptions to their recommended medications. This study thus aimed to assess adherence to antidiabetic medications and determinant factors including medication related beliefs among type 2 diabetic patients attending their treatment in primary healthcare centers of Addis Ababa, Ethiopia using standardized measures. Methodology: A facility-based cross-sectional study design was followed to assess study participants recruited from among type 2 diabetic patients attending their treatment in three health centers in Kirkos Sub City, Addis Ababa from April to June, 2013. For the assessment interviewer administered structured questionnaires based on standardized measures such as the 8-item Morisk"s Medication Adherence Scale (MMAS) and the specific Belief about Medications Questionnaire (BMQ) were used. Result: A total of 155 study participants, all of whom were on oral hypoglycemic agents were involved in the study among whom 53.5% were male and 49.1% had maximum educational status of just being able to read and write. The findings into the medication adherence of the study participants indicated a mean MMAS score of 4.9±2.3 indicative of low adherence. The linear multiple regression model showed the male sex and concern about medications to have negative associations on patients" medication adherence. This might indicate the need for healthcare providers to assess medication-related beliefs and address safety concerns that patients may have.