g-C3N4 nanodots (CNDs) decorated brookite TiO2 quasi nanocube (BTN) is prepared. BTN-CNDs has enhanced CO2-reduction activity as compared to g-C3N4 and BTN alone. Highly dispersed CNDs on BTN surface cause better adsorption capacity of reactants. The CH4 generation selectivity is due to the synergistic effect of CNDs and BTN. Photosensitization is proposed to explain the BTN-CNDs’ CO2-reduction activity.