Context :

Aims : We aim at constraining evolutionary models at low mass and young ages by identifying interesting transiting system members of the nearest OB association to the Sun , Upper Scorpius , targeted by the Kepler mission .

Methods : We produced light curves for M dwarf members of the USco region surveyed during the second campaign of the Kepler K2 mission .
We identified ’ by eye ’ a transiting system , USco J161630.68 - 251220.1 ( = EPIC 203710387 ) with a combined spectral type of M5.25 whose photometric , astrometric , and spectroscopic properties makes it a member of USco .
We conducted an extensive photometric and spectroscopic follow-up of this transiting system with a suite of telescopes and instruments to characterise the properties of each component of the system .

Results : We calculated a transit duration of about 2.42 hours occuring every 2.88 days with a slight difference in transit depth and phase between the two components .
We estimated a mass ratio of 0.922 \pm 0.015 from the semi-amplitudes of the radial velocity curves for each component .
We derived masses of 0.091 \pm 0.005 M _ { \odot } and 0.084 \pm 0.004 M _ { \odot } , radii of 0.388 \pm 0.008 R _ { \odot } and 0.380 \pm 0.008 R _ { \odot } , luminosities of \log ( L/L _ { \odot } ) = - 2.020 _ { -0.121 } ^ { +0.099 } dex and - 2.032 _ { -0.121 } ^ { +0.099 } dex , and effective temperatures of 2901 _ { -172 } ^ { +199 } K and 2908 _ { -172 } ^ { +199 } K for the primary and secondary , respectively .

Conclusions : We present a complete photometric and radial velocity characterisation of the least massive double-line eclipsing binary system in the young USco association with two components close to the stellar/substellar limit .
This system fills in a gap between the least massive eclipsing binaries in the low-mass and substellar regimes at young ages and represents an important addition to constrain evolutionary models at young ages .