In tunnel-coupled quantum wells (QWs) CdTe (20 nm wide) and CdMnTe (8 nm wide) separated by Cd0.88Mg0.Te-12 barrier with a thickness of L-B = 5, 7, 9, and 11 monolayers (MLs), the dependence of electron g-factor on the barrier thickness and temperature is investigated by means of the pump-probe Kerr rotation technique. The renormalization of the electron g-factor occurs due to the s-d exchange interaction of electrons with manganese ions in a magnetic QW. The most change of the electron g-factor value Delta g = 0.25 is registered at the least barrier width of 5 MLs and temperature T = 5 K. In this case, the penetration of the electron wave function from the nonmagnetic QW into the magnetic one is estimated to be 0.6%.