The method of the atomized water injection into the free space of coke oven chamber was studied to decrease the carbon deposits by controlling the atmospheric temperature. After the preliminary examinations, three injection lances were installed among four charging holes of an actual coke oven chamber. When the 1.7 kmol/h of water per lance was injected into the free space, the temperature decreased from 1210 to 1160 K and the carbon formation rate was decreased by 70 % (average in an oven length direction, respectively). A long-term (about two months) injection test showed that the remarkable decreases of the frequency of the manual de-carbonization operation held on the oven top and the incidence of the blockage of the standpipe. It was estimated that the decrease of the carbon deposits was brought not only by the depression of the pyrolysis reaction, but also by the dilution of the carbonization gas and the reduction of the carry-over of fines.