The tests of carbon monoxide sorption on hard coal were carried out mostly at room temperature whereas three hard coal samples were tested also at the temperature of liquid nitrogen - 77.5 K. Prior the tests the coal samples were crushed and separated into three grain sizes. The results of sorption tests demonstrated that there is significant correlation between the level of carbon content within a coal sample and its carbon monoxide sorption ability. Both at room temperature and at the temperature of liquid nitrogen sorption of carbon monoxide takes place mostly across the outer surfaces of coal grains. In the case of coal sample collected in Jaworzno mine, having high micro-porosity share, no clear correlation between grain size of that coal and its sorption ability was observed; that can be attributed to sorption processes occurring in the system of micropores within that particular coal. The specific changes of shapes of isotherms of CO sorption at the liquid nitrogen temperature indicated that condensation of carbon monoxide molecules occurred in the free spaces between coal grains. Such condensation manifests itself by specific changes in isotherm shapes at higher values of relative pressures - p/p0 = 0.8-1.0.