This work reports on a surprising and abnormal increase of the Raman intensity when the probing area is moved to the edge of a mechanically cleaved Si wafer. Our detailed surface structure study based on atomic force microscope and scanning electron microscope rules out any effect from surface morphology. Systematic study of the Raman system focusing effect with a range of µm finds no focusing effect involved in our observed phenomenon. The linewidth, wavenumber, and intensity of the 521 cm−1 peak are obtained and evaluated quantitatively when the testing region is moved from the center to the cleaved edge. When the grain size of crystalline silicon varies from 20 to 10 nm, the Raman intensity of the 521 cm−1 peak is increasing abnormally, by about 100%. Meanwhile, both the linewidth and wavenumber change by about 2 cm−1 and 4 cm−1, respectively. If instrument and surface factors are well controlled/defined, the change of Raman intensity could provide a sensitive and complementary method for grain size characterization in addition to the Raman wavenumber and linewidth methods. Copyright © 2013 John Wiley & Sons, Ltd.