A pinning force acting upon a periodic fluxon chain in a long Josephson junction with a commensurable periodic lattice of local inhomogeneities is calculated by means of a perturbation theory. The pinning force for a single fluxon is also calculated. Dynamics of a chain and of a single fluxon are also studied. The experimental part of the paper reports results of measurements of a critical bias currentIcversus external magnetic fieldH. The measurements have been performed for long overlap Nb‐NbOx‐Pb junctionsIc(H) curve were observed at multiple values ofH. Agreement between the theory and experiment for different spatial periods of the fluxon chain is satisfactory.