In this study, rosehip seeds were activated as biochar (BC) in a tube furnace. Then, BC powder was mixed with hydrothermally synthesized zinc stannate (Zn2SnO4, ZTO) nanoparticles and the resulting mixture was activated by a co-calcination method to fabricate a mesoporous ZTO/BC nanocomposite. The dye removal performance samples were evaluated by measuring the photodegradation of Rhodamine B (RhB) under UV light irradiation. The effects of the catalyst type, dosage of the catalyst, and pH of the aqueous solution were examined to show the nanocomposite’s compatibility. It was found that ZTO/BC nanocomposite containing 15wt% of ZTO showed the strongest photocatalytic activity and could almost entirely degrade RhB (99.4%) after 45 min of UV light irradiation. Both photocatalytic and sorption methods have the ability to effectively remove RhB with ZTO/BC nanocomposite from an aqueous solution. The results of this study exhibit that the proposed nanocomposite system can be effectively used for low dye-concentrated aqueous solutions.