We report magnetization measurements of grain-aligned Ba 2Ca 2Cu 3O 6(O,F) 2 with T c≃108 K. The interlayer distance of the material is the shortest among known tri-layer superconductors. Unexpectedly, the magnetization data show that the coupling strength between CuO 2 layers is rather weak. A direct reflection of the weak coupling is highly suppressed irreversibility line, i.e. a broad reversible region in H– T plane. The decoupling field obtained from the irreversibility line is less than 0.1 T, which is comparable with that of quasi two-dimensional superconductor Bi 2Sr 2CaCu 2O 8+ δ . Comparison of data with the Hao–Clem model gives characteristic parameters [ ξ ab (0) and λ ab (0)] and the critical fields [ H c (0) and H c2 c (0)]. A large value of penetration depth, λ ab (0)=240 nm reflects a small carrier concentration in CuO 2 planes, and explains the reason of the weak interlayer coupling.