Students with Autism Spectrum Disorder (ASD) who lack of social skills have been hindered from being included in IE classrooms. The purpose of this study was to identify the most frequently occurring social skills deficits area among students with ASD in IE classrooms so that the mainstream teachers will be ready and well prepared to cater to their special educational needs (SEN) accordingly in order to yield more effective educational outcomes. A total of 34 teachers in three schools with inclusive classrooms in Johor state, Malaysia were involved in this study. The instrument used in the current study was adapted from TRIAD Social Skills Assessment (TSSA) by Vanderbilt Kennedy Center. The instrument was adapted and consisting of a 41-items survey form which assess the knowledge and skills of students with ASD in three areas, namely cognitive, behavioral and affective. The findings showed the most observed social skills deficits fall under behavioral and affective areas. Comparison of the three areas in social skills using repeated measures analyses indicated that there was a significant difference among the scores of three areas among the students with ASD. The implications of practice were discussed.