The solubility of solid calcium oxalate monohydrate (CaC2O4H2O, COM) has been measured in aqueous solutions of four 1:1 electrolytes (NaCl, KCl, CsCl, and Me4NCl) at temperatures T = 298.15, 323.15, and 343.15 K. Solubilities at industrially relevant electrolyte concentrations of up to 5.0 mol.kg(-1) were determined by atomic absorption spectrophotometry of the dissolved calcium ions. The solubility of COM in 1.0 mol.kg(-1) electrolyte solutions was 2-4 times higher than in pure water but varied little at higher ionic strengths for all of the systems studied. Most of the observed solubilities were well correlated at all temperatures and electrolyte concentrations using a simple Specific Ion-interaction Theory (SIT) model with only one adjustable, temperature-independent, interaction parameter. For Me4NCl solutions, an additional empirical ionic strength dependence of the SIT parameter significantly improved the fit.