Room-temperature P-band emission induced by an exciton-exciton collision process was observed in ZnO micro-rods. Both temperature- and excitation-intensity-dependent photoluminescence (PL) measurements were conducted. The excitation-intensity-dependent measurement illustrated that the P-band emission could occur at far lower excitation intensity than that reported in the literature. Higher-order transitions were also observed at the excitation intensity of 7.1 kW/cm2 or above. The temperature-dependent PL showed that the P-band emission process was thermally activated. It is suggested that both the density and activity of free excitons played important roles in the exciton-exciton collision process.