This paper presents a reference study of available algorithms for plagiarism detection and it develops semantic plagiarism detection algorithm for plagiarism detection in medical research papers by employing the Medical Ontologies available on the World Wide Web. The issue of plagiarism detection in medical research written in natural languages is a complex issue and related exact domain of medical research. There are many used algorithms for plagiarism detection in natural language, which are generally divided into two main categories, the first one is comparison algorithms between files by using fingerprints of files, and files content comparison algorithms, which include strings matching algorithms and text and tree matching algorithms. Recently a lot of research in the field of semantic plagiarism detection algorithms and semantic plagiarism detection algorithms were developed basing of citation analysis models in scientific research. In this research a system for plagiarism detection was developed using “Bing” search engine, where tow type of ontologies used in this system, public ontology as wordNet and many standard international ontologies in medical domain as Diseases ontology which contains a descriptions about diseases and definitions of it and the derivation between diseases.