This study examines the effect of mathematics interventions using Direct Instruction (DI) strategies on the number and operation abilities of students with autism spectrum disorders. Three students (two fourth-grade students and one fifth-grade student) with autism spectrum disorders in S elementary school in Gyeonggi province were the study participants. A multiple probe baseline design across subjects was applied as the research method. A mathematics program that applied the principles of DI, based on the achievement standards in the mathematics “number and operation” unit of the 2015 Special Education Curriculum, was used as the study intervention. To examine the effect of the intervention, progress monitoring was conducted during each session of the intervention, and formation evaluation was conducted for the transition to the next stage. Moreover, the maintenance of the intervention effect was examined two weeks following the termination of the intervention. The study results show that mathematics instruction using DI strategies had a positive effect on the number and operation abilities of students with autism spectrum disorders.