To enhance the reasoning ability successfully in a classroom we implement the new technique. For that the investigator uses the Multimedia package to improve the Mathematics student-teachers in reasoning ability. Multimedia improves the effectiveness of teaching learning process in formal or informal setting and utilizing scientific principle. Multimedia is characterized by the presence of text, pictures, graphics, sound, animation and video; some or all of which are organized into some coherent program. A primary application of the interactive multimedia for instruction is in an instructional situation where the learners is given control so that he/she may review the material at his or her own pace and in keeping with his/her own individual interests, needs, and cognitive processes. The objectives of the study was to measure the effectiveness of the multimedia approach in reasoning ability among Mathematics student teachers and the experimental research is essential for finding out into effective from the population of student teachers, the investigator selected 24 students from a college of education in Tamil Nadu. Tools used were Multimedia package to improve reasoning ability developed by the investigator and Reasoning Ability scale developed by the investigator. In the experimental group, student teachers were taught the subject Mathematics by using this Multimedia package to improve reasoning ability. The control group student teachers were taught traditional method to improve reasoning ability. Findings of the study showed that Control group and experimental group do not differ significantly in their pre-test scores. Control group and experimental group students differ significantly in their post-test scores. Control groups students differ significantly in their pre-test and post-test scores. Also Experimental group students differ significantly in their pre-test and post-test scores. The conclusion of the study was that the experimental group student teachers have achieved high in post- test than the control group so that the reasoning ability was enhanced in the student teachers of experimental group than control group.