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We report results of an extensive world-wide observing campaign devoted tothe recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). Thedata were obtained during the July 2010 eruption of the star and in August andSeptember 2010 when the object was in quiescence. During the July 2010superoutburst SDSS J1625 clearly displayed superhumps with a mean period of$P_{\rm sh}=0.095942(17)$ days ($138.16 \pm 0.02$ min) and a maximum amplitudereaching almost 0.4 mag. The superhump period was not stable, decreasing veryrapidly at a rate of $\dot P = -1.63(14)\cdot 10^{-3}$ at the beginning of thesuperoutburst and increasing at a rate of $\dot P = 2.81(20)\cdot 10^{-4}$ inthe middle phase. At the end of the superoutburst it stabilized around thevalue of $P_{\rm sh}=0.09531(5)$ day. During the first twelve hours of thesuperoutburst a low-amplitude double wave modulation was observed whoseproperties are almost identical to early superhumps observed in WZ Sge stars.The period of early superhumps, the period of modulations observed temporarilyin quiescence and the period derived from radial velocity variations are thesame within measurement errors, allowing us to estimate the most probableorbital period of the binary to be $P_{\rm orb}=0.09111(15)$ days ($131.20 \pm0.22$ min). This value clearly indicates that SDSS J1625 is another dwarf novain the period gap. Knowledge of the orbital and superhump periods allows us toestimate the mass ratio of the system to be $q\approx 0.25$. This high valueposes serious problems both for the thermal and tidal instability (TTI) modeldescribing the behaviour of dwarf novae and for some models explaining theorigin of early superhumps.

SDSS J162520.29+120308.7 - a new SU UMa star in the period gap