Abstract The BL Lac object 4FGL J0955.1+3551 has been suggested as a possible source of ultra energetic neutrinos detected by the Icecube observatory. The target was observed in January 2020 at the Large Binocular Telescope. Our spectroscopy (4100-8500 Å) yields a firm redshift z = 0.557 as deduced by the absorption lines of the host galaxy. The upper limit of the minimum equivalent width on emission lines is ∼0.3 Å. From the source image we are able to resolve the host galaxy for which we measure an absolute magnitude M(R) = -22.9 and Re = 8 kpc, that is values which are typical of the host galaxies of BL Lacs.