A PSII reaction center complex consisting of three polypeptides, D_1, D_2 and Cyt. b_(559), was first purified from broad bean leaves. The complex was fairly active inDCIP photoreduction in the presence of DPC, and showed signal Ⅱs either in the dark or under illumination. The complex also contained manganese atoms. Its Mn~(2+)-EPR intensity decreased by about 40% under continuous illumination and recovered to the original level when the complex was transferred to the dark. The above results indicated that the complex reported here contains all of the PSII electron transport chain components from the secondary donor Z to the stable primary electron acceptor Q_A, and it is possible that the complex contains manganese binding sites. The alternation in dark and illumination can induce reversible valence changes of the manganese atoms in the purified complex.