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Context. Wolf Rayet/black hole binaries are believed to exist as a laterevolutionary product of high-mass X-ray binaries. Hundreds of such binaries mayexist in galaxies, but only a few of them are close enough to be observed asX-ray binaries. Only a couple of candidates have been reported so far. Aims.Based on XMM-Newton observations, we report the positional coincidence of thebrightest X-ray source in NGC 300 (NGC 300 X-1) with a Wolf-Rayet candidate.Temporal and spectral analysis of the X-ray source is performed. Methods. Wedetermine an accurate X-ray position of the object, and derive light curves,spectra and flux in four XMM-Newton observations. Results. The positions of theX-ray source and the helium star candidate coincide within 0.11"+-0.45". TheX-ray light curves show irregular variability. During one XMM-Newtonobservation, the flux increased by about a factor of ten in 10 hours. Thespectrum can be modelled by a power-law with Gamma~2.45 with additionalrelatively weak line emission, notably around 0.95 kev. The mean observed(absorbed) luminosity in the 0.2-10 kev band is ~2x10^38 erg/s. Conclusions.NGC 300 X-1 is a good candidate for a Wolf-Rayet/black-hole X-ray binary: itsposition coincides with a Wolf-Rayet candidate and the unabsorbed X-rayluminosity reached L(0.2-10 kev)~1x10^39 erg/s, suggesting the presence of ablack hole.Comment: 4 pages, 3 figures, accepted as Letter in A&

A Wolf-Rayet/black-hole X-ray binary candidate in NGC 300