The study purported to develop a Teacher-Assisted Multimedia Instructional Package in Physics and to test its effectiveness in enhancing Retention Capacity of Secondary School Students of Kerala. Further, this effectiveness was to be compared with that of the Activity Oriented Method of Instruction. The Quasi Experimental Method with the Pre-Test Post-Test Non Equivalent Groups Design was found to be suitable for the study. The Teacher-Assisted Multimedia Instructional Package and the Activity Oriented Method of Instruction were the independent variables while the Retention Capacity was the dependent variable of the study. The experiment was conducted on a sample of 400 Secondary School Students of Kerala with 200 each in the Experimental and Control Groups. The results of the study showed that the Teacher-Assisted Multimedia Instructional Package in Physics is more effective than the Activity Oriented Method of Instruction in enhancing Retention Capacity of the Students.