The article presents the research into hygienizing process of chicken manure using calcium peroxide (CaO₂) as an environmentally friendly biological deactivation agent. The influence of the addition of CaO₂ to chicken manure on the bioavailability of phosphorus was also analyzed. The process of biological deactivation using CaO₂, CaO and Ca(OH)₂ agents was analyzed applying the disk diffusion method. To optimize the effect of the hygienizing parameters, (CaO₂ concentration, pH, temperature and time) on the reduction of Enterobacteriaceae count the Taguchi method was applied. The content of bioavailable phosphorus was measured with the Egner-Riehm method and determined with spectrophotometry. The reduction in bacterial count followed an increase in the concentration of CaO₂ in a sample. The optimal experimental conditions (CaO₂=10.5 wt.%, pH=9.5, T=40°C, t=180 h) enabled a significant decrease in the Enterobacteriaceae count, from 10⁷ cfu/g to 10² cfu/g. Analysis of the samples with Egner-Riehm method showed that the phosphorus content decreased with the addition of biocide CaO₂: from 26.6 mg/l (for 3.5 wt.%) to 3.5 mg/l (for 10.5 wt.%). These values were slightly higher than the content of phosphorus deactivated with Ca(OH)₂ i.e., from 11.25 mg/l (for 3.5 wt.%) to 4.49 mg/l (for 10.5 wt.%). The application of CaO₂ for hygienizing chicken manure enables effective reduction of Enterobacteriaceae count to an acceptable level (below 1000 cfu/g). In comparison with the traditional techniques of hygienization, the application of CaO₂ has a positive effect on the recovery of bioavailable phosphorus.