The photoreflectance spectra of the 0.4nm diameter single-walled carbon nanotubes (SWNTs) have been measured. The sharp features obtained from the experimental spectra have been identified to be the van Hove singularities associated with tubes of different chiralities, and fitted by the first-order derivatives of both real and imaginary parts of the dielectric functions, such that the band structures of the SWNTs are further clarified. © 2005 The American Physical Society.