This study was carried out to explore learner perceptions on the instructional design features of interactive multimedia (IMM), which was especially designed to support the open and distance learners studying microbiology as a part of the BSc degree programme of the Open University of Sri Lanka (OUSL). The purpose of developing this IMM was to explain the dynamic abstract concepts and processes of bacterial genetics that are hard to comprehend by referring to print course material, as surfaced from course evaluations. When developing the IMM package, emphasis was placed on the interface design, navigational design and instructional design in particular. Instructional design was mainly based on Gagne's nine events of instructions, and Mayer's Cognitive Theory of Multimedia Learning on verbal and pictorial information. IMM was designed incorporating basic instructional features such as learning outcomes, an introduction, self-assessment questions, glossary, and so forth. Animations with narrations were extensively used to explain abstract processes. These design features were integrated, enabling active learning, visualising the dynamic abstract bacterial processes over time, and testing learners' knowledge with immediate feedback, allowing them to achieve a meaningful learning experience. Learner perceptions on instructional design features were gathered through quantitative and qualitative research methods by means of questionnaires, interviews and observations. Evaluation revealed many positive features and a few negative features to be incorporated into the design of IMM in providing better support for the learners. Findings of this study throw light on designing effective learner-centred multimedia learning material. (Contains 6 figures and 2 tables.)