Indoor air-conditioning system (IAS) using wireless sensor network serves to reduce the amount of pollutants entering the room from outside and also the pollutants that are generated indoor. Small-size, low power wireless sensor node and sensor interface board was designed for indoor air-conditioning system in buildings of offices and industrial establishments. Several sensor nodes form an ad-hoc network topology using simple forwarding routing protocol to transmit polluting gas concentration data from different rooms to the indoor air-conditioning system. Sensor node can be efficiently controlled by connecting to a PC for conserving the energy of sensor node using query processing. Sensor node analyzes pollution concentration in each room and air-conditioning system performs to air-distribution and air-inhalation according to room's pollution by regulating the fan of indoor air-conditioning system. To reduce power consumption, an electrochemical gas sensor is used in the design. Thus the designed system is able to optimize the state of indoor environment.