In this study, we present a systematic investigation of the relationship between the reaction conditions and product selectivity as applicable to glucose photoreforming. Nickel titanate (NiTiO3) nanorods were synthesized to examine the photocatalytic oxidation of glucose to value-added products at various substrate concentrations, reaction times, solvent pH values, solvent compositions, and reaction atmospheres. Varying the reaction conditions yielded two distinct glucose valorization pathways, producing arabinose and organic acids, respectively. We obtained up to 75% selectivity for arabinose in neutral conditions and 63% selectivity for organic acids─lactic acid, acetic acid, and formic acid─in alkaline conditions. Finally, we propose mechanisms for the selective production of value-added chemicals via glucose photoreforming by NiTiO3 and investigate the optimal conditions for arabinose production. This work demonstrates the complex dependence of glucose photoreforming on reaction conditions and the potential of reaction engineering to unlock selective photocatalytic mechanisms for biomass-derived substrates.