Minimum Zone Evaluation of Cylindricity by Optimization Techniques Tadao TSUKADA and Tohru KANADA This report represents optimization techniques to evaluate the cylindicity according to ISO and JIS. Such the direct search methods as improved simplex method and Powell's method were applied and the algorithms were studied. Consequently, it was made clear that the new algorithm for improved simplex method, which was developed in this research, was the most effective from the view point of the calculation time and the accuracy of cylindricity.