Abstract: OBJECTIVE To investigate the effect of the concentration of the suspending aid Avicel^® in a suspension nasal spray on the spray pattern, plume geometry and droplet size of nasal spray. METHODS Preparation of Fluticasone furoate nasal suspension with different concentration of Avicel^®. Through SprayVIEW^® spray test system to test the spray characteristic parameters of nasal spray, and Box-Behnken response surface method was used to analyze the influence of Avicel^® concentration on the spray characteristics of nasal spray in vitro. At the same time, the influence of Avicel^® concentration on the distribution of spray droplet size and the change of droplet size at different detection distances were investigated. RESULTS Increasing the concentration of the Avicel^® would significantly reduce the spray area, spray angle and width(P<0.001), while increasing D₅₀ and overall particle size. It was also found that increasing the actuation velocity would significantly increase the spray area, spray angle and width(P<0.05), and the influence of actuation acceleration on spray characteristics was far less than that of Avicel^® concentration and actuation velocity. As the detection distance increased, the droplet size distribution become more concentrated and the span of droplet size distribution become smaller. CONCLUSION In this study, Box-Behnken response surface method is used to observe the antagonistic effects of Avicel^® concentration and actuation velocity on spray characteristics, which provides a reference for the selection of Avicel^® concentration for nasal sprays as well as the recommended actuation parameters for the device.