The authors report the room temperature gas sensitivity of ultrathin SnO2 films prepared by thermal decomposition of multilayer Langmuir-Blodgett (LB) films. The SnO2 films, which are characterized by various spectroscopic techniques and electrical measurements, have been shown to sense ammonia gas at room temperature with fast response and recovery. The presence of a large number of surface states in the ultrathin SnO2 film is responsible for the room temperature gas sensitivity. Present results demonstrate the potential of LB technique to fabricate high quality ultrathin oxide films useful for sensor applications.