The cyclotron mass of electrons in Cd1-xMnxTe has been found to be remarkably larger than that in CdTe at very high magnetic fields around 100 T. The degree of an enhancement of the mass Delta m* obtained experimentally is about twice as large as Delta m* calculated with the k.p theory. We found that the large spin splitting of the Landau levels due to the s(p)-d exchange interaction has only a small effect on the cyclotron mass. Other effects caused by the electron-phonon interaction, some impurities and applying very strong fields are likely to be important to understand the large mass enhancement in Cd1-xMnxTe.