Background: In Chile, the mortality rate from colorectal cancer has been increasing rapidly. The Prevention Project for Neoplasia of the Colon and Rectum (PRENEC) program was introduced in 2012 with intense support from Tokyo Medical and Dental University (TMDU) in Japan, as part of an international collaboration. Japanese experts in colonoscopy have been dispatched from TMDU to Chile, not only to perform colonoscopy, but also to teach Chilean trainees how to perform colonoscopy in PRENEC. This study assesses the efficacy of the training system in colonoscopy under the guidance of a Japanese expert in PRENEC. Methods: From March 2016 to August 2017, a Japanese expert (board certified endoscopist in Japan) taught 13 trainees. All trainees were beginners who had no prior experience performing a colonoscopy. In PRENEC, the trainees follow a step-by-step process for learning colonoscopy, which is described as follows: Firstly, trainees acquire the strategy for insertion and observation through attending lectures and observing actual colonoscopies performed by a Japanese expert. Secondly, trainees repeatedly practice the strategy with colon model simulator. Thirdly, trainees start performing actual colonoscopies with direct hands-on support until they are able to handle the colonoscope as instructed. Finally, trainees perform colonoscopies by themselves with mostly verbal guidance from a Japanese expert. We divided all colonoscopies into 3 groups. The groups were separated by operators as follows: group A by 13 trainees under the guidance of a Japanese expert; group B by a Japanese expert; and group C by 16 experienced Chilean colonoscopists. We assessed each group's quality by the success rates of total colonoscopy, complication (perforation and bleeding) rates, and adenoma detection rates (ADR). In addition, we assessed the self-completion rates of total colonoscopy by 5 trainees who had learned colonoscopy for 3 consecutive months at the 1st, 2nd and 3rd month, respectively. Results: A total of 1568 colonoscopies were performed during this period, which consisted of 443 in group A, 146 in group B and 979 in group C. In group A, B and C, mean patient age was 65.0AE7.5/63.2AE7.8/63.0AE7.1 years, respectively (no significant difference [NS]). Male/female ratio (%) was 30.7/25.9/53.2 (NS). Success rates of total colonoscopy (%) were 99.5/99.3/96.6 (group A vs Group B [NS], group A, B>group C p<0.01). Complication rates (%) were 0.45/0.00/0.34 (NS). ADR (%) were 66.6/64.4/40.0 (group A vs group B [NS], group A, B>group C p<0.01). Mean self-completion rates of total colonoscopy (%) at the 1st, 2nd and 3rd month by the 5 trainees were 56.5AE19.6/66.5AE26.1/86.4AE12.9, respectively. Conclusion: The colonoscopy training system in PRENEC was effective because trainees were able to steadily improve their skills in short periods of time without sacrificing clinical outcomes.