Background: The standard national protocol for treatment of acute lymphoblastic leukemia (ALL) in children was implemented in 2006. A systematic evaluation of the treatment outcome is needed. This study examined the relapse-free survival among childhood ALL cases treated with this protocol and related factors. Materials and Methods: A descriptive study was conducted in children aged between 0-15 years, newly diagnosed with ALL between March 2006 and March 2011 at Srinagarind Hospital, Department of Pediatrics, Faculty of Medicine, Khon Kaen University. The patients were treated on the basis of stratified risk as per the Thai national protocol. Data were compiled from the hospital records. The Kaplan-Meier method was used to describe relapse-free survival and the Cox proportional hazard model to investigate the associated factors. Results: Of the 103 children recruited, 86 (83.5%) achieved complete remission. The total follow-up time was 3132.5 person-months. Eighteen (20.9%) relapsed. The incidence density was 0.6 per 100 person-months (95%CI: 0.4, 0.9). The respective relapse-free rates at 1, 3 and 5 years were 93.0% (95%CI: 85.1, 96.8), 84.5% (95%CI: 74.0, 90.9) and 64.1% (95%CI: 45.6, 77.8). A factor associated with the relapse-free rate was age under 1 year (HR=6.0; 95%CI: 1.1, 33.8). Conclusions: The rate of being relapse-free in ALL children treated under the Thai national protocol at Srinagarind Hospital was better than with former protocols; however, it is still not as good as in developed countries. Further review of the treatment approach of ALL is needed.