The purpose of this study was to identify students' changes of (i) interest toward STEM subjects and (ii) interest to pursuing STEM career after participating in non-formal integrated STEM education programme. The programme exposed students with integrated STEM education through project based learning involving the application of five phases engineering design process. Two cohorts of middle secondary students participated in 2014 (n=129) and 2015 (n=113) were involved in this study. The study utilized one group quasi-experimental design. The analysis revealed that, overall there is a significant increase in mean scores for interest towards STEM subjects and career after participating in the programme. The findings also indicated that the program was effective at modifying students' interest level as the result revealed positive changes (from moderate to high level) for both 2014 and 2015 groups for interest toward STEM career (42.6% and 69.9% respectively) and interest towards STEM subjects (45% and 82% respectively).