The resistive transition of a preferentially oriented thin film of Y2Ba4Cu8O16‐δ has been measured in fields up to 20 T oriented parallel to the c‐axis. The data can be analysed in terms of thermally activated flux flow and flux pinning due to dislocation lines. The analysis yields the upper critical field Bc2 which shows an unusual upward curvature at low temperatures. Furthermore an estimate can be made of the correlation length Lc of the flux line lattice in the field direction. Lc is found to be very small, however, remaining larger than the Cu02 plane distance.