Аннотация:An investigation was made into crystal structure and magnetic properties of rare earth manganese silicides LaxCe1-xMnSi. Magnetization measurements were conducted in static magnetic fields up to 13kOe within the range of 77 to 460K. It was found that at 0≤x≤0.5 these compounds are antiferromagnetics and at higher lanthanum content-ferromagnetics with Curie point of 292-301K. Transition from ferromagnetic to antiferromagnetic state at lanthanum content variations occurs at the certain critical value of lattice parameter A1 through which a distance between the nearest neighbours inside manganese layers may be calculated. This transition is related to variation of localization degree of 3d-electrons.