In framework of classical consideration of electron trajectories in crossed E, H fields and con-ductivity of electron system on cyclotron resonance in single layer graphene possibility to achieve THz cyclotron lasing in hexagonal boron nitride–single layer graphene sandwiches is discussed. By simplified consideration with known data on scattering rate in the sandwiches it is demonstrated that the CW laser action can be achieved in high quality sandwiches at room temperature at frequencies above about 0.5–1 THz in magnetic field above 5000–10000 Gauss. Short discussions of Landau level quantization in crossed fields, amplification on cy-clotron harmonics and cyclotron amplification at low temperatures are given.