Thermal buckling analysis of functionally graded spherical shells with geometrical imperfection is presented in this article. It is assumed that the material properties of functionally graded spherical shell are changed by a power law function through the thickness of shell. The equilibrium and stability equations of an imperfect functionally graded spherical shell are derived using the Donnell-Mushtari-Velasov theory (DMV). Approximate solutions considered for displacement components are based on the assumption that they satisfy the boundary conditions. The Galerkin method is used to minimize the errors caused by using the approximation. Three various types of thermal loadings including the uniform temperature rise (UTR), linear radial temperature rise (LTR), and the nonlinear radial temperature rise (NTR) are assumed for analytical solution. The results are validated with the known data in literature.