Fuzzy logic is widely used as the fundamental platform for the many artificial intelligence-based systems like control of subways, air conditioners, transmission systems, facial pattern recognition, antiskid braking systems. In the theory of fuzzy set, membership functions (MFs) provide an infrastructure for determining the degree of truth in a fuzzy model. So, they can play important role in the performance of these logical mechanisms. Different types of MF can be defined to fuzzification-defuzzification process (i.e. converting Boolean input to a fuzzy output and vise-versa). They are categorized and named based on the shape of their diagrams as triangular, Gaussian, trapezoidal and so forth. In the current study the effect of MF's type on the search capability of Interactive Search Algorithm (ISA) is assessed. To meet this aim, a metaheuristic technique that are known as Interactive Search Algorithm and strengthen with fuzzy adjustment mechanism is tested on solving a number of benchmark problems involving different types of MFs. The results indicate that due to stochastic essence of metaheuristic approaches the type of MF does not seriously affect the search capability of this technique. Therefore, it can be stated that the MFs should be selected based on the simplicity criterion. In other words, the simplest MF which provides the designers requirements can be the best choice.