Pure and boron modified Ag3PO4 powders with different boron contents (0–5 wt.%) were prepared. XRD, ATR-FTIR, XPS, SEM-EDX, UV-Vis DRS and PL analyses were conducted for the characterization of the prepared powders. Characterization studies indicated the reduction in the band gap energy, the presence of boron and no change in the morphology due to boron modification. The results of photocatalytic experiments showed that boron modification increased the activity of Ag3PO4. The UV light dye degradation efficiency increased from 63% to 84% for methyl orange (MO) and from 41% to 65% for methyl red by 3% boron modification. The reaction rate constant for MO increased by a factor of 1.7. Under visible light, the activity was similarly enhanced by boron modification. The photocatalytic degradation efficiency increased from 31% to 58% and the reaction rate constant increased by a factor of 2.3 by boron modification for MO under low intensity visible light. These results showed that boron modification enhanced the photocatalytic dye degradation activity of Ag3PO4 under both UV and visible light. This enhancement was attributed to the decrease in the band gap energy and the increase in the interaction of the dye molecules with the photocatalyst surface through boron species.