Context : A significant number of the Wolf-Rayet stars seem to be binary or multiple systems , but the nature of many of them is still unknown .
Dedicated monitoring of WR stars favours the discovery of new systems .

Aims : We explore the possibility that WR62a is a binary system .

Methods : We analysed the spectra of WR62a , obtained between 2002 and 2010 , to look for radial-velocity and spectral variations that would suggest there is a binary component .
We searched for periodicities in the measured radial velocities and determined orbital solutions .
A period search was also performed on the “ All-Sky Automated Survey ” photometry .

Results : We find that WR62a is a double-lined spectroscopic binary with a WN5 primary star and an O 5.5-6 type secondary component in orbit with a period of 9.1447 d. The minimum masses range between 21 and 23 M _ { \odot } for the WN star and between 39 and 42 M _ { \odot } for the O-type star , thus indicating that the WN star is less massive than the O-type component .
We detect a phase shift in the radial-velocity curve of the He ii \lambda 4686 emission line relative to the other emission line curves .
The equivalent width of this emission line shows a minimum value when the WN star passes in front of the system .
The analysis of the ASAS photometry confirms the spectroscopic periodicity , presenting a minimum at the same phase .

Conclusions :