Nowadays, the application of computer technology in assisting the classroom teaching and learning is common and popular, particularly in special education. Many researches have indicated the inherent value and significance of using CAL in teaching children with special educational needs (SEN). It has been stated that the computer may serve the communicative, instructional, training, recreational, learning or adaptive purposes. School success in applying the technology depends on many factors but familiarity and proficiency of teachers to the increasing demand of such technology are essential elements. However, there is not much available literature illustrating the use of computers in mentally handicapped schools in Hong Kong. The purposes of this paper are to investigate the instructional use of the computers and the difficulties encountered in different types of mentally handicapped schools. The research has been carried out in different types of mentally handicapped schools in Hong Kong. By questionnaire, the resources, facilities and frequencies of use in computers have been identified. Variables such as school types, school policy, budget, teacher attitude and commitment and instructional practices were identified and their contribution to the effectiveness of the program have been examined. By the follow-up case studies in the three different categories of mentally handicapped schools, an in-depth study on the organizational factors, teachers' attitude and commitment, pupils needs and instructional practices have been investigated. Such quantitative and qualitative analysis aimed at illustrating a clear picture about the use of resources in the classrooms. The results indicated that nearly all the mentally handicapped schools used the computers in teaching their SEN students. However, the students encountered different sorts of difficulties in using the computers, owing to their physical and intellectual disabilities. It was found that some of the teaching activities