Structural modulations in solid solutions of C,S doped with various amounts of ZnO were investigated via the selected-area electron diffraction method. Three monoclinic modifications (M(I), M(II), and M(III)) were identified in the solid solutions. The modifications had pseudohexagonal subcells that were modulated to form supercells. Coordinates of the reflections attributable to the supercells could be expressed by the following linear combinations of vectors of the reciprocal lattices: m(1)(-2a*/5.4 + 2b*/5.4 - 7c*/5.4) for M(I), m(2)(-a*/5 + b*/5 - c*) for M(II), and m(3)(-a*/6 + b*/6 + 7c*/6) for M(III), m, and m(2) = +/-1 and +/-2, and m(3) = +/-1, +/-2, and +/-3. All the monoclinic modifications possessed structural modulations of a one-dimensional type. The modulation waves could be detected as wavy contrasts by high-resolution transmission electron microscopy.