Control systems are progressing day by day and providing new methods in order to improve the obtained results. Fuzzy systems, which are one of the best control methods, are widely used in various applications today. With the improvements made in these systems, a new type of these systems called type-2 fuzzy systems was proposed. Due to their more up-to-date structure which have more control parameters than the type-1 fuzzy system, these systems can provide better results than this systems. Like other systems, the stability of these systems is a fundamental challenge in control systems. In this paper, the necessary and sufficient conditions for the stability of two classes of type-2 fuzzy systems are considered. At first, a class of type-2 TSK fuzzy systems with a linear "then" section and then a nonlinear "then" section are examined. It should be noted that in this paper, type 2 TSK fuzzy systems are considered as open loops. In the simulation section, two stable and unstable type 2 fuzzy systems are investigated and as shown, the results confirm the correctness of the analysis.