  Double-lined spectroscopic binary systems, containing a Wolf-Rayet and a
massive O-type star, are key objects for the study of massive star evolution
because these kinds of systems allow the determination of fundamental
astrophysical parameters of their components. We have performed spectroscopic
observations of the star WR 68a as part of a dedicated monitoring program of WR
stars to discover new binary systems. We identified spectral lines of the two
components of the system and disentangled the spectra. We measured the radial
velocities in the separated spectra and determined the orbital solution. We
discovered that WR 68a is a double- lined spectroscopic binary with an orbital
period of 5.2207 days, very small or null eccentricity, and inclination ranging
between 75 and 85 deg. We classified the binary components as WN6 and O5.5-6.
The WN star is less massive than the O-type star with minimum masses of 15 +/-
5 Msun and 30 +/- 4 Msun , respectively. The equivalent width of the He II
{\lambda}4686 emission line shows variations with the orbital phase, presenting
a minimum when the WN star is in front of the system. The light curve
constructed from available photometric data presents minima in both
conjunctions of the system
