The main purpose of the present study was to investigate the teachers‟ professional knowledge and its practice at secondary level in Khyber Pakhtunkhwa. In professional knowledge teachers‟ know their subject contents and how to teach those contents to their students. Teachers also focus on the action or process of teaching as well as the knowledge and skills gained through experience. Objectives of the study were: (i) To investigate the teachers‟ professional knowledge and its practice at secondary level; (ii) To examine the factors that affect the teachers‟ professional knowledge and its practice at secondary level; (iii) To find out what are the difficulties in the implementation of teachers‟ professional knowledge and its practice; and (iv) To compare the views of working teachers and prospective teachers regarding teachers‟ professional knowledge and its practice. For achieving the objectives of the study the following null hypotheses were tested; (i) There is no significant difference between teachers‟ professional knowledge and its practice; (ii) There is no significant effect of environmental factors on teachers‟ professional knowledge and its practice; (iii) There is no significant difference between difficulties and teachers‟ professional knowledge, its practices and implementation; and (iv) There is no significant difference between the views of working teachers and prospective teachers regarding teachers‟ professional knowledge and its practice. The population of the study was comprised of all the 210 prospective teachers who were enrolled as students of B.Ed (130) and M.Ed (80) in Northern University Nowshera (NUN) and all the 18683 (SST) male teachers at secondary level of Government Secondary Schools in the province of Khyber Pakhtunkhwa. A convenient sample of 105 prospective teachers from Northern University Nowshera (NUN) and 600 male working teachers from Khyber Pakhtunkhwa were selected through convenient sampling technique. The data were collected from xviii B.Ed and M.Ed classes of Northern University Nowshera (NUN) and from five Districts of Khyber Pakhtunkhwa: D.I.khan, Haripur, Mardan, Nowshera and Swabi. Three point questionnaires were used as research instrument for collection of data from the sample teachers. Chi-square technique was used to analyze the data statistically. The study was significant for all stakeholders in education including teachers, students, educational authorities and policy makers.