The preparation of large MCM-41 single crystals as well as their controllable morphologies has very important meanings not only for their potential applications but also for the exploration of the new morphogenetic mechanism for some special mesoporous crystals. In this paper, a novel crystal form of hexagonal circular bicone of MCM-41 crystal, which is the combination form of thee hexagonal bipyramid and circular bicone forms, has been observed. The MCM-41 single crystals which originally remained the same can grow larger to nearly ∼10 micron via multiple-growth in extremely diluted ammonia solution, and were characterized by SEM, POM, TEM, XRDetc. The morphology of the MCM-41 crystal can also be controllably modulated by adding alkali salts to the synthetic system. Increasing the concentration of KCl can cause the aspect ratio and the conical angle to increase consistently and the result displays monotonicity with a certain statistical deviation. A fluctuation effect has an influence on the surface energy and eventually leads to the evolution from a single crystal to one with non-crystalline characteristics.