Plagiarism is prohibited and a violation of copyright. Based on the Regulation of the Minister of National Education, Republic of Indonesia, 2010, whom who done plagiarism may be the subject of punishment in the form of a reprimand to cancellation of diploma students who has graduated. The efforts that can be taken to prevent plagiarism is to detect the occurrence of plagiarism using string matching algorithms such as Boyer Moore, Brute Forte, Knuth Morris Pratt (KMP), and Rabin-Karp. The most effective algorithm Rabin-Karp algorithm that uses the functions k-gram to determine the length of the string and the pattern pieces hash function to change any pattern string into a numeric value and then comparing the level of similarity source text with the comparison text. The Case studies in Payakumbuh College Technology is done through sampling data in the form of proposals title which are submitted by Computer Engineering student. To detect the plagiarism is done by comparing the sample pieces source documents and comparison sample pieces document. Testing process on 4 stages, they are: preprocessing, tokenizing k-gram, fingerprint and similarity calculation. The research result is the similariy value precentage on comparison of text A and text B also text A and text C in k-gram value is 3, 4 and 5 then basis value on 3, 5 and 11 which better done on k-gram value=3 and basic value 3 they are 78.16% for comparition of text A and B then 78,79 for comparition of text A and text C.