Provided is a process of producing cyclohexanone oxime comprising the steps of: pre-mixing an inorganic process solution containing a high concentration of hydroxylamine phosphate with a first stream of cyclohexanone such that the concentration of hydroxylamine phosphate is reduced to 80% or less of its initial concentration; and subjecting hydroxylamine phosphate in the premixed inorganic process solution to an oximation reaction with a second stream of cyclohexanone. According to the process, oximation is performed after the inorganic process solution containing a high concentration of hydroxylamine phosphate has been pre-mixed with the first stream of cyclohexanone to reduce the concentration of hydroxylamine phosphate. As a result, not only that the efficiency of oximation and the yield of cyclohexanone oxime are increased, but also the organic content of the inorganic process solution discharged from the oximation tower is reduced.