The purpose of this study was to explore parent involvement of mentally retarded students in elementary schools, whether parents of children with mental retardation and special education teachers would differ in their attitudes toward parent involvement, and factors related to parent involvement. There were 104 special education teachers, and 276 parents of children with mental retardation in Taiwan north area were investigated with researcher-designed questionnaire. Data was analyzed by mean, standard deviation, ANOVA, and MANOVA. The findings of this study were as follows: (1) “Learning at home” was the most involvement style for parents of children with mental retardation. “Volunteering and decision-making” was found to be the least involvement style. The involvement needs for parents of children with mental retardation showed the same results. (2) Parents of children with mental retardation and special education teachers had positive and affirmative attitudes toward parent involvement. Special education teachers were found to show more positive attitudes toward parent involvement than parents significantly. (3) Mothers’ education levels and marriage statuses were reported to be the crucial factors associated with parent involvement. Therefore, recommendations were made in terms of administrators and teachers.