Abstract Cold Atmospheric Plasma (CAP) has been studied for years in the context of cancer therapy where it presents efficient properties on inducing cell death. Reactive Oxygen and Nitrogen Species (RONS) through oxidative stress are reported to justify treatment effect on tumor but biological mechanisms involved are not fully understood. As cold plasma is very effective on producing RONS but with very complex chemical kinetics, this study proposes to measure concentrations of some species formed in the gas and aqueous phase to offer a comprehension of chemical interactions that could lead to an increase of cold plasma cancer treatment efficiency. Anticancer effect after exposition to CAP has been demonstrated on a prostate tumor cells line for both direct and indirect treatment. To determine RONS concentrations in both gas phase and liquid phase, an experimental reactor was developed for different methods of analysis to be conducted in similar conditions and potentially simultaneously. In gas phase, ozone and nitrogen oxides have been evaluated and the influence of some physical parameters on their concentrations has been demonstrated through a design of experiments. In pure water, nitrates, hydrogen peroxide, hydroxyl radical and singlet oxygen have been produced, but in culture medium, a significant concentration has been measured only for hydrogen peroxide. Culture medium components appeared to scavenge the most reactive species. Future investigations will interest in other key species, in physical parameters influence on RONS production in liquid phase and also in adjustment of medium composition to prevent the effect of scavenging.