Magnetic monopoles are predicted in various unified gauge models and could be produced at intermediate mass scales .
Their detection in a neutrino telescope is facilitated by the large amount of light emitted compared to that from muons .
This paper reports on a search for upgoing relativistic magnetic monopoles with the ANTARES neutrino telescope using a data set of 116 days of live time taken from December 2007 to December 2008 .
The one observed event is consistent with the expected atmospheric neutrino and muon background , leading to a 90 % C.L .
upper limit on the monopole flux between 1.3 \times 10 ^ { -17 } and 8.9 \times 10 ^ { -17 } cm ^ { -2 } s ^ { -1 } sr ^ { -1 } for monopoles with velocity \beta \geq 0.625 .