  We report the identification of the optical counterpart to the transient
ultraluminuos X-ray source in the blue dwarf galaxy UGC6456 (VII Zw 403). The
source is highly variable in both the X-ray (more 100 times, 0.3-10 keV) and
optical (more 3 times, V band) ranges. The peak X-ray luminosity of UGC6456 ULX
exceeds $10^{40}$ erg/s; the absolute magnitude when the source is optically
bright is M$_V = -8.24\pm0.11$, which makes this source one of the brightest
ULXs in the optical range. We found a correlation between the optical and X-ray
fluxes (with a coefficient of $0.9\pm 0.3$), which may indicate that the
optical emission is produced by re-processing of the X-rays in outer parts of
the optically-thick wind coming from the supercritical accretion disk. Optical
spectra of UGC6456 ULX show broad and variable hydrogen and helium emission
lines, which also confirms the presence of the strong wind.
