Copper sludge is produced during the production of printed circuit boards. The leaching of copper from the sludge by the NH3-(NH4)2SO4 system was studied. First, the mass contents of heavy metals in the sludge were determined. With few contents of other metals, the content of copper was 33.500％. The effect of concentrations of NH3-(NH4)2SO4, pH, leaching time, liquid／solid ratio and temperature were investigated. The optimum leaching conditions were found when the ammonia／ammonium sulfate concentrations were 3.0mol／L and 1.5mol／L, the leaching time was 180min, the liquid／solid ratio was 20mL／g, and the temperature was 25℃. Under these conditions, about 97.5％ of the copper was effectively leached, and the relative standard deviation(RSD) was 0.63％.