  Through time-series CCD photometry of the globular cluster NGC 5466, we have
detected nine SX Phoenicis stars including three new ones. All the SX Phoenicis
stars are located in the blue straggler region in the color-magnitude diagram
of NGC 5466. Five of them show clearly double-radial mode features, the periods
of which are well consistent with the theoretical ratio of the first overtone
mode to the fundamental mode (P$_{1H}$/P$_F$). Normally, it has not been easy
to secure a P-L relation of the SX Phoenicis stars, because determination of
the pulsational mode of the SX Phoenicis stars has been difficult. The
existence of five SX Phoenicis stars in NGC5466 with double-radial modes allows
us to derive reliably a P-L relation for the fundamental mode of the SX
Phoenicis stars. Using seven SX Phoenicis stars including five stars with
double-radial modes, we derive a P-L relation for the fundamental mode in NGC
5466, $<V> = - 3.25 (\pm 0.46) Log P + 14.70 (\pm 0.06), (\sigma = \pm0.04) $,
corresponding to $<M_V> = - 3.25 (\pm0.46)Log P - 1.30 (\pm0.06) $ for an
adopted distance modulus of $(m-M)_0=16.00$ and zero reddening.
