Here we present HST/ACS imaging , in the B and I bands , of the edge-on Sb/Sc galaxy NGC 5170 .
Excluding the central disk region region , we detect a 142 objects with colours and sizes typical of globular clusters ( GCs ) .
Our main result is the discovery of a ‘ blue tilt ’ ( a mass-metallicity relation ) , at the 3 \sigma level , in the metal-poor GC subpopulation of this Milky Way like galaxy .
The tilt is consistent with that seen in massive elliptical galaxies and with the self enrichment model of Bailin & Harris .
For a linear mass-metallicity relation , the tilt has the form Z \sim L ^ { 0.42 \pm 0.13 } .
We derive a total GC system population of 600 \pm 100 , making it much richer than the Milky Way .
However when this number is normalised by the host galaxy luminosity or stellar mass it is similar to that of M31 .
Finally , we report the presence of a potential Ultra Compact Dwarf of size \sim 6 pc and luminosity M _ { I } \sim –12.5 , assuming it is physically associated with NGC 5170 .