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The magnetic relaxation in a Tl2Ba2Ca2Cu3O10±x superconducting thin film has been measured at a range of temperatures (5–70 K) and field strengths (500–5000 Oe). Measurements reveal that the relaxation obeys a logarithmic time dependence in the time interval 2000 s<t<12 000 s. The relaxation rate is both temperature and field dependent. The average pinning potential U* calculated from the relationship U*=kT/[(-1/Mi)dM/d lnt] is in the range 20–70 meV, which is similar to those of Y-Ba-Cu-O and (Bi,Pb)-Sr-Ca-Cu-O. The anomalous increase of U* at higher temperature is found to be closely related to the irreversibility line.