The electrochemical behavior of Mo4O11 single crystals has been studied and periodic phenomena were observed during anodic dissolution in 1M H2SO4. These periodic effects were observed only on the (100) face, and are associated with a 12.3Å periodicity in the crystal structure along the  direction, where alternating layers of Mo (IV) and Mo (VI) species are found. A mechanism involving the slow chemical dissolution of Mo (VI) species and the rapid electrochemical dissolution of Mo (IV) species is offered, and is consistent with the experimental data. To the best of our knowledge, this is the first reported correlation of a periodic electrochemical effect with a periodicity in the crystal structure. © 1976, The Electrochemical Society, Inc. All rights reserved.