  We report CCD V and I time series photometry of the globular cluster NGC 5024
(M53). The technique of difference image analysis has been used which enables
photometric precisions better than 10 mmag for stars brighter than V 18.5mag
even in the crowded central regions of the cluster. The high photometric
precision has resulted in the discovery of two new RR1 stars and thirteen SX
Phe stars. A detailed identification chart is given for all the variable stars
in the field of our images of the cluster. Periodicities were calculated for
all RR Lyraes and SX Phe stars and a critical comparison is made with previous
determinations.
  Out of four probable SX Phe variables reported by Dekany & Kovacs (2009), the
SX Phe nature is confirmed only for V80, V81 is an unlikely case while V82 and
V83 remain as dubious cases. Previous misidentifications of three variables are
corrected. Astrometric positions with an uncertainty of ~ 0.3 arcsec are
provided for all variables.
  The light curve Fourier decomposition of RR0 and RR1 is discussed, we find a
mean metallicity of [Fe/H]=-1.92+-0.06 in the scale of Zinn & West from 19 RR0
stars. The true distance moduli 16.36+-0.05 and 16.28+-0.07 and the
corresponding distances 18.7+-0.4 and 18.0+-0.5 kpc are found from the RR0 and
RR1 stars respectively. These values are in agreement with the theoretical
period-luminosity relations for RR Lyrae stars in the I band and with recent
luminosity determinations for the RR Lyrae stars in the LMC.
  The age of 13.25+-0.50 Gyr (Dotter et al. 2010), for NGC 5024, E(B-V)=0.02
and the above physical parameters of the cluster, as indicated from the RR0
stars, produce a good isochrone fitting to the observed CMD.
  The PL relation for SX Phe stars in NGC 5024 in the V and I bands is
discussed in the light of the 13 newly found SX Phe stars and their pulsation
mode is identified in most cases.
