In this manuscript we investigate the impact of oxalate ions on the crystallization of barium sulfate. The organic anion, oxalate, was found to inhibit both nucleation and growth according to atomic force microscopy measurements and dynamic light scattering data. Raman confocal imaging was used to try and determine how the oxalate interacts with the barium sulfate surface. It was found that barium oxalate is only seen at very high oxalate concentrations. At lower concentrations no direct evidence for the presence of oxalate was observed, however, the most probable mode of action for oxalate is via adsorption onto the barium sulfate surface including into key kink or step sites, impacting growth.