The different morphology and size of the zinc oxide (ZnO) were synthesized by a co-precipitation process via variation of calcination temperature from 400 °C to 900 °C. The nanorod, flower, hexagon, pentagon, and microflambeau morphologies were obtained. The flower morphology of ZnO tends to inactivate multidrug-resistant Pseudomonas aeruginosa (P. aeruginosa) completely within 45 min under solar light irradiation better than other morphologies due to efficient separation electron-hole pairs. The prevention of charge recombination was confirmed by transient photocurrent response and electrochemical impedance spectra measurements. Electron spin resonance spectroscopy suggests that [Formula: see text] OH·, and h+ are responsible for P. aeruginosa inactivation in solar light. Furthermore, P. aeruginosa inactivation was confirmed by transmission electron microscope (TEM) images, DNA fragmentation (gel electrophoresis) and protein degradation (Bradford assay). The TEM mapping illustrates the damage of bacteria by active species but not the release of Zn2+ ions in the bacterial cell. So, this work provides a detailed investigation of morphology/size-dependent photocatalytic inactivation of a multidrug-resistant pathogen in solar light.