Context :

Aims : We aim at detecting and determining the properties of the host galaxy of the dark GRB 050223 .

Methods : We use VLT optical/NIR images coupled to Swift X-ray positioning , and optical spectra of the host galaxy to measure its properties .

Results : We find a single galaxy within the Swift error box of GRB 050223 .
It is located at z = 0.584 and its luminosity is L \sim 0.4 L ^ { * } .
Emission lines in the galaxy spectrum imply an intrinsic { SFR } > 7 M _ { \sun } yr ^ { -1 } , and a large extinction A _ { V } > 2 mag within it .
We also detect absorption lines , which reveal an underlying stellar population with an age between 40 Myr and 1.5 Gyr .

Conclusions : The identification of a host galaxy with atypical properties using only the X-ray transient suggests that a bias may be present in the former sample of host galaxies .
Dust obscuration together with intrinsic faintness are the most probable causes for the darkness of this burst .