For the purpose of practical application of the adsorptive desiccant cooling system using a honeycomb rotor dehumidifier, a 20 kw field-test apparatus has been carried out. Effects of operating conditions and ambient air conditions on performance of the adsorptive desiccant cooling system are investigated, and the following results are obtained; 1) The optimum air temperature Tg for regeneration of the adsorbent rotor is found to maximize the thermal coefficient of performance. When the temperature and absolute humidity of ambient air are T-1 = 28.4 similar to 32.3 degrees C, X-1 = 8.8 similar to 11.7 g/kg, the optimum air temperature for regeneration is around T-8 = 65 similar to 85 degrees C. 2) The cooling capacity is found to decrease with increasing absolute humidity of ambient air. 3) At regeneration air temperature above 100 degrees C, the thermal coefficient of performance is improved significantly when the flow rate ratio of regeneration air to supply air through the dehumidifier is selected as one-half. 4) The cooling performance is estimated to be improved by using a water spray heat exchanger instead of the conventional evaporative cooler.