The B4508 is a rural B-road along the Vale of White Horse. It was originally unclassified but gained its number in the mid-1930s.
The road starts on the A420 between Southmoor and Kingston Bagpuize and heads southwestwards, skirting the grounds of Pusey House before narrowing to go through the small village. We continue across the fields on fairly flat land, bearing sharply right before going through Hatford and presently reaching the A417, which is crossed at a staggered crossroads.
Continuing southwestwards we run through Shellingford before deviating from our route to follow a winding course through Fernham. We regain our southwesterly course by the village green then skirt Longcot to reach a crossroads. Originally the B4508 continued ahead from here and passed to the south of Watchfield to end on the then-A420 Shrivenham High Street. However, following the construction of the Watchfield and Shrivenham bypass in the late 1980s the road ahead was declassified and the B4508 rerouted along formerly unclassified roads to the west. We therefore TOTSO right and follow a gentle curve left to a roundabout on the A420 Watchfield bypass.
There's a short multiplex west and the B4508 turns right to regain its number. The road continues west past a small wind farm and then crosses a weak bridge over the River Cole. The road now narrows, presumably to dissuade traffic from crossing the bridge, and continues on to end at a triangular junction on the B4000.