The ionization produced by electrons having energies of several tens of electron volts in the nighttime Venusian atmosphere is investigated on the basis of plasma measurements made on board Venera 9 and 10. We conclude that electron fluxes are sufficient to produce a nighttime ionosphere with a maximal electron density of 104 cm-3. Calculated density profiles of the Venusian nighttime ionosphere show shapes closely resembling measured ones with closely agreeing values of maximal density and corresponding altitudes as well.