This paper reports the numerical investigation of the quantum confinement effects on excitons in a Si cylindrical core/shell quantum dots. Using the effective-mass approximation and considering a variational technique, we have calculated the exciton ground state binding energy as functions of the shell size in order to study the behavior of the confined exciton into the region of a thin shell with rigid walls. Our results show that the core-shell sizes have a remarkable influence on the electron-hole interaction, which leads to a significant impact on the binding and the optical photoluminescence energies of exciton. Also, we found that the exciton binding energy is higher for the small shell sizes. The effects caused by quantum confinement in such quantum dot nanostructures offer an alternative way of tuning the excitonic transitions in optoelectronic semiconducting devices.