Heating of the ionosphere due to incidence of electromagnetic pulses coming from lightning discharges has been theoretically investigated. The electromagnetic radiation from lightning discharges produces variation in ionizing frequencyand effective collision frequency of electrons. The energy gained by the free electrons from the incident electric fields of wide-band electromagnetic pulses from lightning strikes is not instantaneously transferred to the heavy particles in the medium, due to which the electron temperature is raised. Variation of temperature increase has been estimated.