Aim: The study was conducted for the purpose of determining managerial competency levels of nursing supervisors and the factors affecting these levels of competence. Method: Of the crosssectional design, the research was conducted over the period October-December 2015 with 124 consenting nursing supervisors working in public, university and private hospitals (6 hospitals) located in the provinces of Balıkesir and Sakarya. A Personal Questionnaire on individual characteristics and a "Nursing Supervisor Competency Evaluation Inventory" (NSCEI) were used in the collection of data. Scored on a scale of 1-5, the inventory was assumed to be an equal interval scale and each interval was given a value of 0.80. Scores of 3.40 and below on the inventory items were accepted as indicating a lack of competence and a need for training. The data was analyzed using numbers, percentages t test, one-way analysis of variance, and Tukey's test. Results: It was found that 50.8% of the nursing supervisors had master's degrees, 45.2% had 16 years or more of nursing experience, 72.6% had 1-5 years of experience in management, 80.6% had not participated in a managerial training program and 86.3% expressed the desire to participate in a managerial training program. The mean NSCEI score was 4.32±.45 and levels of competence varied according to the institution, the individuals were working in, their educational status, and their knowledge about the laws and of job descriptions. It was observed that nursing supervisors perceived themselves as being less competent in the areas of "making changes for improving nursing services," "planning nursing careers," "making use of research in nursing care," and "using an appropriate model of providing nursing care." Conclusion: The majority of nursing supervisors perceived themselves as competent but their levels of competence displayed differences according to the institution they worked in, their educational status, and their knowledge about the laws and of job descriptions.