Professional teacher is one of fundamental factors that influences students' success in learning. Therefore, identifying influencing factors can give insight to improve the teachers' professionalism efficiently. The research aims to measure two internal factors, namely meaning in life and teacher leadership, in influencing teacher professionalism. Quantitative with a cross-sectional survey was further applied using explanatory research to examine private junior high school teachers in Balikpapan, East Kalimantan, Indonesia. Using a random sampling technique, 150 teachers was selected as samples. The data were then analyzed through structural equation modeling with smartPLS version 3.3.0. The measurement proved that meaning in life positively influenced the teachers' professionalism and teacher's leadership with a p-value of 0.000 and T-statistic for each is 8.094 and 6.887, respectively. Similarly, teacher leadership positively influences teacher professionalism, with a p-value of 0.000 and T-statistics of 4.554. Besides, meaning in life through teacher leadership contributes to teacher professionalism with a p-value of 0.000. These results recommended the meaning in life and teacher leadership as the internal factors in planning the teacher professional development policy because, to date, the focus was only on the external factor.