This explanatory sequential study investigated secondary school principals' perceptions on barriers regarding the Information and Communication Technology (ICT) integration in a developing country, Indonesia. For the quantitative phase, we administered a survey instrument to 250 Indonesian secondary school principals. The survey instrument was developed based on previous related literature validated through content validity and piloted before being distributed. Following the quantitative process, three Focus Group Discussions (FGDs) with 30 participants were conducted to obtain more in-depth information. Each FGD was attended by 10 participants. The findings revealed that the most highly identified barriers are teachers' knowledge of ICT, funding for ICT, traditional teaching style, professional development, as well as district and school culture. Recommendations are offered for the improvement of technology integration for educational purpose.