We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 ( SDSS J1625 ) .
The data were obtained during the July 2010 eruption of the star and in August and September 2010 when the object was in quiescence .
During the July 2010 superoutburst SDSS J1625 clearly displayed superhumps with a mean period of P _ { sh } = 0.095942 ( 17 ) days ( 138.16 \pm 0.02 min ) and a maximum amplitude reaching almost 0.4 mag .
The superhump period was not stable , decreasing very rapidly at a rate of \dot { P } = -1.63 ( 14 ) \cdot 10 ^ { -3 } at the beginning of the superoutburst and increasing at a rate of \dot { P } = 2.81 ( 20 ) \cdot 10 ^ { -4 } in the middle phase .
At the end of the superoutburst it stabilized around the value of P _ { sh } = 0.09531 ( 5 ) day .

During the first twelve hours of the superoutburst a low-amplitude double wave modulation was observed whose properties are almost identical to early superhumps observed in WZ Sge stars .
The period of early superhumps , the period of modulations observed temporarily in quiescence and the period derived from radial velocity variations are the same within measurement errors , allowing us to estimate the most probable orbital period of the binary to be P _ { orb } = 0.09111 ( 15 ) days ( 131.20 \pm 0.22 min ) .
This value clearly indicates that SDSS J1625 is another dwarf nova in the period gap .
Knowledge of the orbital and superhump periods allows us to estimate the mass ratio of the system to be q \approx 0.25 .
This high value poses serious problems both for the thermal and tidal instability ( TTI ) model describing the behaviour of dwarf novae and for some models explaining the origin of early superhumps .