EPR examination of cellulose carbonized at 400◦C and 600◦C has been performed. The aim of this work was to search a sample useful as the oximetric probe in biology and medicine. The higher paramagnetic centers concentration characterizes cellulose carbonized at 600◦C, which was found as the sensitive oximetric probe. Quasi-chemical bonds between cellulose molecules and paramagnetic O2 molecules decrease paramagnetic centers concentration. A linear increase in paramagnetic centers concentration and a linear decrease in EPR linewidth with increasing time of sample evacuation were observed for cellulose carbonized at 600◦C. Oxygen affects spin–lattice interactions in carbonized cellulose.