Abstract: We present an investigation for a particle confined in an infinite well with sinusoidal bottom, using the perturbation theory and numerical solution for the Schrödinger equation to obtain the eigen energies and wavefunctions. Potential strength and potential oscillation dependence of the state are examined and analyzed. It is shown that the particle in a box with sinusoidal bottom does not show up the Klauder phenomenon when the perturbations are gradually reduced to zero. The research results show that the potential oscillation significantly affects certain quantum states and, therefore, the ability to manipulate the energy difference between the states. In addition, our results for the present system converge to their corresponding values for the unperturbed one in the high-potential oscillation limit. Keywords: Infinite well, Perturbation theory, Sinusoidal potential, Numerical calculations, Klauder phenomenon.