According to the observational limits on the radius and mass, the fastest r
otating pulsar (PSR 1937+21) is probably a strange star, or at least some n
eutron star equations of state should be ruled out, if we suggest that a di
pole magnetic field is relevant to its radio emission. We presume that the
millisecond pulsar is a strange star with much low mass, small radius and w
eak magnetic moment.