This paper presents the free vibration analysis of stiffened isotropic plate by means of finite element method. Stiffeners are used in plates to increase the strength and stiffness. The effect of position of stiffeners on isotropic plate has been studied which involve the possible combination of clamped and free edge condition. The model has been discretized using a 20-node solid element (SOLID186) from the ANSYS element library. The natural frequencies are calculated using Block-Lanczos algorithm. The comparisons of stiffened plate with the available results are found to be in good uniformity. The effect of different boundary conditions, stiffeners location, thickness ratio, stiffener thickness to plate thickness and aspect ratio on the vibration analysis of stiffened plates has been studied.