Through time-series CCD photometry of the metal-poor globular cluster M53 , we have discovered eight new SX Phoenicis type stars ( labeled from SXP1 to SXP8 ) .
All the new SX Phoenicis stars are located in the blue straggler star region of a color-magnitude diagram of M53 .
One of these stars ( SXP2 ) is found to have very closely separated pulsation frequencies : f _ { 1 } / f _ { 2 } = 0.9595 
where f _ { 1 } and f _ { 2 } are primary and secondary frequencies .
This may be due to excitation of non-radial modes .
Six of these SX Phoenicis stars are considered to be pulsating in the fundamental mode .
They show a tight linear correlation between the period and luminosity .
We derive a period - luminosity relation for the fundamental mode for the period range of -1.36 < LogP [ d ] < -1.15 : < V > = -3.010 ( \pm 0.262 ) LogP + 15.310 ( \pm 0.048 ) with an rms scatter of 0.038 , corresponding to < M _ { V } > = -3.010 LogP - 1.070 for an adopted distance modulus of ( m - M ) _ { V } = 16.38 ( Harris 1996 ) .