We report the kinetic analysis of radicals on fungal spores of Penicillium digitatum interacted with charged-neutral oxygen species (O*) generated plasma discharge using real time in situ electron spin resonance (ESR) measurements. The ESR signal from the spores was observed at a g-value of around 2.004 with a line width of approximately 5G. We have successfully obtained information regarding the reaction mechanism with free radicals and realtime in situ ESR has proven to be a useful method to elucidate plasma-induced surface reactions on biological specimens