SnOxfilms with different values ofxwere deposited by rf sputtering. Secondary emission yield &dgr;, physical density &ggr;, and electrical resistivity &rgr; of the films were investigated. Higher values of &dgr; than those of bulk SnO and SnO2were found. From the experiment it results that &dgr;, &ggr;, and &rgr; increase with the increase ofx. The crossover energyEc, the primary electron energy for &dgr;=1, decreases withx. Analysis of the experimental data and theory leads to the conclusion that the main factor which determines the maximum secondary electron emission yield &dgr;mis the ratio between the escape probability and the work function.