Context : Rotation and magnetic activity are intimately linked in main-sequence stars of G or later spectral types .
The presence and level of magnetic activity depend on stellar rotation , and rotation itself is strongly influenced by strength and topology of the magnetic fields .
Open clusters represent especially useful targets to investigate the rotation/activity/age connection .
Over the time stellar activity and rotation evolve , providing us with a promising diagnostic tool to determine age of the field stars .

Aims : The open cluster M11 has been studied as a part of the RACE-OC project ( R otation and AC tivity E volution in O pen C lusters ) , which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters with different ages .

Methods : Photometric observations of the open cluster M11 were carried out in June 2004 using LOAO 1m telescope .
The rotation periods of the cluster members are determined by Fourier analysis of photometric data time series .
We further investigated the relations between the surface activity , characterized by the light curve amplitude , and rotation .

Results : We have discovered a total of 75 periodic variables in the M11 FoV , of which 38 are candidate cluster members .
Specifically , among cluster members we discovered 6 early-type , 2 eclipsing binaries and 30 bona-fide single periodic late-type variables .
Considering the rotation periods of 16 G-type members of the almost coeval 200-Myr M34 cluster , we could determine the rotation period distribution from a more numerous sample of 46 single G stars at an age of about 200-230 Myr and determine a median rotation period P=4.8d .

Conclusions : A comparison with the younger M35 cluster ( \sim 150 Myr ) and with the older M37 cluster ( \sim 550 Myr ) shows that G stars rotate slower than younger M35 stars and faster than older M37 stars .
The measured variation of the median rotation period is consistent with the scenario of rotational braking of main-sequence spotted stars as they age .
Finally , G-type M11 members have a level of photospheric magnetic activity , as measured by light curve amplitude , comparable to that observed in the in younger 110-Myr Pleiades stars of similar mass and rotation .