Effects of the strength of the geomagnetic main field on the electrodynamics of the ionosphere were studied. Electric conductivities of the ionosphere were estimated for the cases of three times, normal, and 1/10 strength of the main field. It was shown that when the field strength decreases, altitudes of Pedersen conductivity maxima shift upward, and height-integrated Pedersen and Hall conductivities are enhanced. The electric potential difference and currents of the ionospheric dynamo were also simulated for the above three cases. Weakening of the geomagnetic main field decreases the potential difference because of the smaller induction field. However, the reduction is not as large as that of the main field because the dynamo region is lifted and effective neutral wind velocity becomes large. On the contrary, height-integrated ionospheric currents are enhanced because the current intensity is essentially determined by the product of the electron density and the neutral wind velocity in the dynamo region. Lower gyrofrequencies of electrons and ions due to the weak main field shift the dynamo region upward to the altitudes where the electron density and the wind velocity are larger. ¿ American Geophysical Union 1996