In the present work, we introduce a facile and widely used route to fabricate Cu₂O nanocrystal/titanate nanobelt heterojunctions with high yield, good dispersion and tight interaction, and which are self-assembled via the linker molecule 3-mercaptopropionic acid. Their photocatalytic activity for the degradation of methyl orange solution is enhanced by decorating with Cu₂O nanocrystals, especially in the visible light region. The degradation rates of 6 wt% Cu₂O/titanate heterojunctions are both the highest at 100% after 80 and 180 minutes irradiation under UV and visible light irradiation, while those of the pure titanate nanobelts are only 20% and 3%, respectively. These lower values for the pure titanate nanobelts are due to the p–n heterojunctions suppressing the recombination of electron–hole pairs in the titanate nanobelts, where the Cu₂O nanocrystals act as electron traps aiding electron–hole separation. Additionally, a synergistic effect from the tight contact between Cu₂O nanocrystals and titanate nanobelts also efficiently enhances the photodegradation of the Cu₂O/titanate heterojunctions.