The main purpose of this study was to determine the impact of metacognition skills instruction on secondary school girl students’ selfefficacy.A quasi experimental research method was used. The statistical population (N=520) comprised all grade three secondary school girl students studying Humanities in Hamedan city. Using a cluster sampling method, two classes and 70 subjects were selected as the study sample. The instrument used for data collection was the Sherer self-efficacy assesment scale. The validity of the questionnaire has been reported as acceptable. The reliability of the instrument computed through Cronbach’s alpha was 0.81. Data were analyzed using descriptive indices, such as the frequency, mean, standard deviation, and inferential tests such as the independent t-test, analysis of covariance and one-way analysis of variance. Findings show that goal centring, goal penetration, internal motivation, problem solving skills and self evalution of the students who recieved metacognition instruction were greater than those of students not receiving such instruction.