Microalgae cultivation is a light-demanding process. Optimal growth of microalgae takes place in appropriate reactors. In this research the effects of the light intensity and the reactor geometry on the yield of microalgae Nannochloropsis salina in an internally-illuminated bubble-column photobioreactor was investigated. An axisymmetric two-dimensional phenomenological model of the reactor comprising gas-phase and liquid-phase mass balances was utilized. Axial and radial dispersion correlations in gas and liquid phases were applied on the description of the non-ideal flows in the reactor. The model was validated against the experimental data obtained in a reactor with 0.1 m in the diameter of the smaller cylinder, 0.197 m in the diameter of the larger cylinder, 0.8 m in the culture height, and being fed by a gas of 2% CO2-air ratio with the flow rate being 800 mL/min for 15 days. The validation result shows that the model can reproduce well the experimental results with 5% error. The microalgae yield produced in the reactor with the diameter of the larger cylinder of 0.197 m is 0.52 g/L. It decreases when the diameter of the larger cylinder enlarges. Increasing the intensity up to 22.5 W/m2 raises the microalgae production. However, increasing the intensity beyond that value reduces the microalgae production.