Characteristic effects of magnetic ordering and conduction in semiconductor heterostructures with a GaAs : Be/Ga_0.84In_0.16As/GaAs quantum well and manganese δ-layers of different thickness (from 0.4 to 2 monolayers) were studied based on analysis of magnetic field and temperature dependences, galvanomagnetic effects, and magnetization. An anomalous dependence of the conductivity on the manganese atoms concentration in the δ-layer was observed, which was due to a strong scattering of charge carriers in the structures with the low content of magnetic impurities. Magnetic properties of the heterostructures clearly indicated the magnetic ordering of the impurity system (saturation and hysteresis of the magnetization and fulfillment of the Curie–Weiss law at increasing temperature). Parameters of the magnetic subsystem allowed revealing different types of ordering in the systems with different concentrations of the magnetic impurity. Changing the concentration of the Mn admixture in the δ-layer was shown to influence significantly the conductivity and magnetism in the studied structures.