Here we examined the equilibrium distribution ratios of copper(II) and ammonia between an ammonium salt solution (nitrate, sulfate, or chloride) and the extractant LIX84I (active component, 2-hydroxy-5-nonylacetophenone oxime) dissolved in a non-polar diluent Shellsol D70 at pH 2–10 and 298 K. The effects of pH, ammonium salt concentration in the aqueous phase, counter anion type, and phase ratio on the co-extraction of copper and ammonia were investigated. The values of the extraction constant of ammonia and the distribution constant of copper-oxime complex were independent of the type and concentration of ammonium salt, and the logarithm of the extraction constant of copper linearly increased with the ionic strength of the aqueous phase. Consequently, we constructed an equilibrium model that enabled quantitative calculation of the distribution ratios of copper and ammonia at a given equilibrium pH. Full loading of copper was found to minimize the accumulation of ammonia in the organic phase, which may reduce the need for ammonia scrubbing in practical operations.