  We present multi-color CCD photometry of the neglected contact binary XZ Leo.
Completely covered VRI band light curves and four times of minimum light were
obtained. Combining the photometric and previously published radial velocity
data, a revised photometric analysis was carried out for the binary system by
applying the Wilson-Devinney code. With a hot spot placed on the massive
primary component near the neck region of the common envelope, the light curves
were satisfactorily modeled. The photometric solution combined with the radial
velocity solution reveals that XZ Leo is an A-type contact binary with a degree
of contact of 24($\pm1)\%$. The absolute parameters of the components were
determined as M_1 = 1.74($\pm$0.06)M_\odot, M_2 = 0.61($\pm$0.02)M_\odot, R_1 =
1.69($\pm$0.01)R_\odot, R_2 = 1.07($\pm0.01$)R_\odot, L_1 = 6.73($\pm0.08$)
L_\odot, L_2 = 2.40($\pm$0.04)L_\odot. Based on all the available data, the
long-term orbital period behavior of the system was investigated. It indicates
that the binary system was undergoing continuous orbital period increase in the
past three decades with a rate of dP/dt = + 6.12 \times {10^{-8}} days yr^{-1},
which suggests a probable mass transfer from the secondary to the primary
component at a rate of dM/dt= 3.92\times 10^{-8} M_\odot yr^{-1}. The binary
system is expected to evolve into the broken-contact stage in $1.56 \times
10^6$ years. This could be evidence supporting the Thermal Relaxation
Oscillation theory.
