This mixed-methods study employed an explanatory sequential design to examine the effect of the blended-mentoring supervision toward science teaching competencies. The studied group comprised 3 pre-service science teachers who were studying in the Faculty of Education at a University in Pattani, Thailand. During 4 months of science teaching practicum in Southern Thai provinces, they were supervised under the designed blended-mentoring supervision by supervisors and in-service science teachers. A science teaching competency assessment form along with semi-structured interview was used to examine science teaching competency examining from lesson plans, teaching observation notes and teaching material. Then data were analyzed in teaching-competency mean scores in conjunction with content analysis to identify the change of teaching competency. The findings revealed that the teaching competencies of the 3 pre-service science teachers were at high level with "learning management capacity" being the highest, followed by "teacher's comprehension of the taught science content and level," and "measurement and assessment ability" with 4.08, 4.07, and 3.98 mean scores, respectively. The interview and observation analysis revealed that the influencing factors of the science teaching competencies comprise pre-class mentoring, teaching observation, reflection, and technological integration for the blended-mentoring process.