NOVELTY - An aqueous solution containing potassium hydroxide is heated, and solution (b) of oxalic acid and sodium nitrite is added to aqueous solution containing potassium hydroxide and filtered, to obtain filtrate and precipitate (p1). The filtrate is concentrated to form precipitate (p2). The precipitate (p2) is cooled, washed and dried, to obtain potassium nitrite. The precipitate (p1) is washed and dried, to obtain sodium oxalate. Potassium nitrite is added to hot water and filtered. The filtered mixture is concentrate, cooled, dried, washed and dried, to obtain potassium nitrite.    USE - Environmentally-friendly co-preparation of potassium nitrite and sodium oxalate (claimed).    ADVANTAGE - The method enables environmentally-friendly co-preparation of sodium oxalate and potassium nitrite with high solubility, with reduced temperature change.    DETAILED DESCRIPTION - Potassium hydroxide and oxalic acid in weight ratio of 1.5-1.6:1 are added to a container, mixed and filtered, to obtain 20-30% aqueous solution containing potassium hydroxide. Oxalic acid with content of 1.6 weight times of sodium nitrite is added to 40-60 wt.% aqueous solution containing sodium nitrite and filtered, to form solution (b). The aqueous solution containing potassium hydroxide is heated at 85 degrees C, and solution (b) is added to aqueous solution containing potassium hydroxide with stirring, and maintained at 80 degrees C for 0.5 hour. The mixture is filtered and collected, to obtain filtrate and precipitate (p1). The filtrate is concentrated at 80 degrees C to form precipitate (p2). The precipitate (p2) is cooled, washed with water and dried, to obtain industrial-grade potassium nitrite. The precipitate (p1) is washed twice with water and dried at 100 degrees C, to obtain analytically-pure sodium oxalate. Industrial-grade potassium nitrite is added to hot water at 80 degrees C such that the ratio of industrial-grade potassium nitrite and hot water is 3-4:2 and filtered. The filtered mixture is concentrated at 80 degrees C to form precipitate. The heating of mixture is stopped, and the mixture is cooled to room temperature, dried, washed with cold water, and dried at 80 degrees C, to obtain analytically-pure potassium nitrite.