The opinion of an expert witness is an important aspect in the law of evidence. As opposed to general witnesses testifying in court on perceived facts, expert witnesses testify based on their area of expertise. Such expert opinions on specific area of expertise assists the court in understanding special or scientific issues beyond the knowledge of common people. This article adopts the doctrine of pure legal research as its framework. Adopting a qualitative approach, methodologies of content analysis and critical analysis are used in analyzing archived materials. This article discusses on the relevancy and admissibility of evidence provided by medical expert witnesses in Malaysia. Special attention is given to Malaysian syariah illicit intercourse cases. The opinions of the four mazhabs on this area of law are highlighted. This writing further dissects the current Shari'ah legislations in Malaysia and compares them with the Malaysian civil legislations. During analysis, the authors find that there are definitely gaps in the current Malaysian Shari'ah evidence enactments. These gaps must be ironed out if we are to witness a better implementation of shari'ah evidential principles regarding expert witnesses during syariah court trials in future.