Abstract Composite material consists of two or more components at the microscopic level, which improves its properties. In recent year, it is widely used in Thermo mechanical loading where the structural performances of these capacities are required to perform at elevated temperature. The consideration of such loading with high temperature is known as thermo mechanical loading, and this type of loading in which thermal and mechanical loading are applied together. In this paper the buckling analysis of composite rectangular plate with combined in-plane mechanical & thermal loading has been carried out. The analysis is performed using the ANSYS APDL software package, in which SHELL element is used. The effects of temperature on the plate have been investigated. It was found from the analysis that the natural frequencies of a variable thickness rectangular plate decrease with the increase of the temperature. Effect of ply angle for different condition is also analyzed and represented with 2D graphs for the effective comparison of various conditions. The load carrying capacity increases with increasing number of ply, at the maximum carrying capacity of load i.e. forty five degree orientation of the plate and shell. If the number of elemental length increases load carrying capacity also increases. Buckling analysis is widely useful in the aerospace industry, in the shipbuilding industry, manufacturing industry therefore the ANSYS FEA software is a good tool for the calculation of critical buckling load.