The temperature dependence of demagnetization curve, intrinsic coercivity and magnetic viscosity has been measured on single crystal Dy (Fe0.8Al0.2)2 in [100], [110] and [111] directions. The staircase and a large jump of demagnetization curve, an obvious peak of coercivity vs temperature, and the magnetic viscosity being independent of the temperature etc., were observed. The observed features were analyzed within the theory of the macroscopic quantum effects for domain walls tunneling in the single crystal. A crossover temperature has been observed at Tcr=5.5K between classical thermal activation and quantum tunneling regimes.