It is becoming a new trend in developing countries to integrate ICT effectively in the teaching-learning process inside or outside the classroom to boost teachers' professional knowledge (TPK). The present study addresses the technology integration relationship with TPK according to the International Society for Technology in Education (ISTE-2008) Standards for Teachers in private secondary schools of Karachi. TPK was categorized as 2 standards of ISTE-2008 i.e. enhance creativity in students and design digital-age assessment. 120 teachers from 12 private secondary schools of Karachi were selected based on a simple random sampling technique. For the collection of data, a teacher survey questionnaire was used that was designed to gain information on their level of ICT integration and their professional knowledge according to the ISTE-2008 Standards. Data was collected through questionnaire distribution and analyzed through SPSS. Based on ANOVA results, the overall model was significant because the F value was greater than 2 and the significant value was less than 0.05. A strong significant correlation was found between ICT integration and TPK. Strong and moderate significant correlation of ICT integration with teachers' ability to enhance creativity and design digital-age assessment was found respectively. ICT integration explained 32% of the variance in teachers' professional knowledge. The integration of ICT with ISTE-standards is highly recommended for the teachers.