We report the temperature and filed dependence of magnetic behaviour of the Ho1-xMmxCo2 (x = 0, 0.1, 0.2, 0.3 and 0.4; Mm = mischmetal) alloys and their crystalline hydrides. The change of magnetic transition temperature (TC), order of magnetic transition and total magnetization of the alloys with increasing Mm content is studied. The alloys exhibit strong composition and field dependence of thermal hysteresis and spin-reorientation below TC. The effect of hydrogen absorption on the magnetic behaviour of alloys is studied, and the results are correlated to the unit cell volume expansion and decrease in the conduction electron density. © 2010 Elsevier B.V. All rights reserved.