  Some modern models of neutron star evolution predict that initially large
magnetic fields rapidly decay down to some saturation value $\sim {\rm
few}\times 0^{13}$ G and weaker magnetic fields do not decay significantly
(Pons). It is difficult to check the predictions of this model for initially
highly magnetized objects on the time scale of a few million years. We propose
to use Be/X-ray binaries for this purpose. We apply several methods to estimate
magnetic fields of neutron stars in these accreting systems using the data
obtained by the RXTE satellite (Galache). Only using the most modern approach
for estimating the magnetic field strengths of long period NSs as proposed by
Shakura we are able to obtain a field distribution compatible with predictions
of the theoretical model of field decay of Pons.
