This paper traces the role of assessment in science education as available in developing countries. It stresses the need to redefine the assessment system in order to infuse a sense of professionalism and competence in Science graduates. The method of assessment must integrate with the instructional objectives through criterion referenced testing. To improve the teaching - learning process, due weightage need to be given for both fornative assessment and surnrnative assessment. In order to measure the attainment of experimental skills and cognitive abilities, both process assessment and product assessment are to be utilised. Although the principles of assessment are mentioned in this part with special teference to a Science laboratory course offered in tertiary level through Distance Education mode, we shall explain the application of the suggested methodology of assessment in the next part.