The present study was an attempt to find out the effectiveness of inquiry approach for addressing the misconceptions of students in Mathematics at secondary level. It is a well-known fact that students enter in classroom with a lot of misconceptions in Mathematics, which are based on their beliefs and observations. The main objectives of this research study were to identify the students’ misconceptions in Mathematics at secondary level, to find out the causes of students’ misconceptions in Mathematics at secondary level, to compare the level of misconceptions in boys and girls at secondary level, to apply the conceptual change instructional strategy based on inquiry approach in class room and to find out the effectiveness of inquiry approach as conceptual change instructional strategy for addressing the students’ misconceptions in Mathematics. The nature of the research study was experimental and pre-test, post-test control group design was used. The population of the study was all the secondary school students of District Attock. The two schools were purposively selected for study. 160 science students (80male and 80 female) of 9th Grade from each school were constituted as a random sample of the study. Students of each school were divided into two equivalent groups of male and female students i.e. control and experimental group on the basis of Pre-test achievements. Achievement test was used to explore misconceptions of the students after validation of the instrument. The Mathematics teachers with equal qualification and experience were trained for the said purpose. In each gender group one teacher taught control group and one teacher taught to experimental group. In control group traditional method was used and experimental group was taught by inquiry based approach. To find out the causes of misconceptions questionnaire was used. Post-test was administered after treatment to assess the difference in performance of all groups. After administration of three weeks of post-test, retention-test was also conducted. The data obtained was tabulated as well as analyzed to compute mean, standard deviation, chi-square and t-value. From results of the data, conclusions were drawn and recommendations were made accordingly. The results depict that inquiry based method found to be better than of traditional method. This result is in the line with Abdi (2014) and the level of misconceptions of female students was found higher than of male students. It was recommended that there may be separate and well equipped classroom for Mathematics teaching in the schools like Physics, Chemistry and Biology to develop the interest of students in Mathematics. Sufficient time may be reserved in time table for the subject of Mathematics, as mathematics is time needed subjects.