This study aims to find out the effect of PBL with procedural scaffolding toward high-order thinking skills in terms of students' high and low ability. This research used non equivalent control group design with 34 students of experimental class and 35 students of control class. The hypothesis test of this study used Two-Way ANOVA and showed that the effect of PBL with procedural scaffolding was 42.5%, while the effect of students' initial ability was 37.9%. The mean posttest grade of the experimental class is higher than the control class, indicating that PBL with procedural scaffolding affects students' high-order thinking skill.