The uniformity and ordering of the surface of (Al)MCM-41 channel walls was investigated employing bare Co(II) ions as probes. VIS spectra of Co(II) ions evidenced the presence of two types of uniform cationic sites in dehydrated Co-(Al)MCM-41 in a wide range of Si/Al/Co chemical composition (Si/Al = 11-76, Co/Al = 0.08-0.44). These cationic sites represent centers of two types of uniform domains, containing in minimum 18 surface T atoms, present on the surface of the channel walls of (Al)MCM-41. These domains represent majority of the inner surface of the (Al)MCM-41 molecular sieve.