The project team gathered data with the assistance of Recreational and Cultural Organization of Mashhad Municipality, Organization of Mashhad Municipality and Science and Astronomy Science Center of Mashhad Municipality, Khorasan Razavi, Islamic Republic of Iran. This paper discusses the effect of science center on attitude of students who visit it. Previous research identified key variables that are fundamental to free-choice science learning. The samples consist of 1002 students of grades 9, 10 and 11 studying in high schools. Before and after the students visited the science center, they filled a questionnaire about their attitude toward science. Results showed that visiting the science center improved the students' attitude towards science. Based on the criterion of attitude growth and gender difference, male's attitude was improved more than female's. Moreover, there were significant differences between students in grade 11, 10 and 9. In addition, Univariate analysis of variance (ANOVA) indicated that the grade and gender difference had significant effect on criterion of attitude growth.