One important aspect of the complex sprinkler protection process is the interaction between the water spray and the fire plume. In order to provide suitable data for the development and validation of a LES-based fire protection models, such as FireFOAM, a series of small-scale experiments were conducted to examine the interaction of hot air plumes and water sprays through combined gas–liquid velocity and droplet size measurements. Laser-based particle image velocimetry (PIV) was used to acquire the spatially-resolved velocity data; and a shadow imaging system (SIS) was used to measure the water droplet size and volume flux. Hot air plumes with three convective heat release rates (1.6, 2.1 and 2.6kW) were selected to interact with a water spray at a discharge rate of 0.084Lpm. The velocity field of the hot air plume and ceiling flow with/without water spray, the droplet size and volume flux of water spray with/without hot air plume were measured. The interaction between the hot air plume and water spray was characterized by the location of the interaction boundary with the momentum ratio of the hot air to that of the spray. The results showed that that the momentum ratio and the evaporation effect due to hot air on the water droplets played a significant role to change the interaction structure and the ceiling layer pattern.