Low teacher professionalism in State Senior High Schools in Barito Kuala Regency is caused by instructional leadership, school atmosphere, and job motivation, thus this study aims to increase teacher professionalism. This study examines how Principal Instructional Leadership, School Climate, and Work Motivation affect Teacher Professionalism in Barito Kuala Regency Public High Schools. This study uses descriptive quantitative methods and a route analysis model (Part Analysis) to analyse variable influences. Probability Sample Random Sampling was used to sample 145 of 228 state teachers in Barito Kuala Regency's state high schools. SPSS 20 was used to descriptively and inferentially analyse questionnaire and documentation data. The regression coefficient of the principal's instructional leadership variable on teacher professionalism was 0.283. School climate favouring teacher professionalism 0.248. Work motivation on teacher professionalism 0.434. Principal instructional leadership on school atmosphere 0.748. On work motivation, the principal's instructional leadership was 0.871, and indirectly: Principal teaching on teacher professionalism via school atmosphere had a leadership 0.178 path coefficient. Principal instructional leadership towards teacher professionalism via job motivation had a 0.730 path coefficient. This research found that the principal's instructional leadership, school climate, and work motivation at Barito Kuala Regency Public High School are high, while teacher professionalism is very high. The principal's instructional leadership, school atmosphere, and job motivation somewhat affect teacher professionalism in Barito Kuala Regency state high schools. The principal's instructional leadership indirectly affects teacher professionalism via school atmosphere and job motivation in Barito Kuala Regency state high schools. The suggestions demand more teacher professionalism, notably pedagogical ability.