Integrated-optical dual-channel multi/demultiplexers with a wavelength periodic transmission characteristic are fabricated on X-cut LiNbO3. The devices are designed for the wavelength range λ = 1300-1600nm. Channel separations as low as 30nm, far-end crosstalk attenuation up to 40dB and an insertion loss of fibre-coupled devices below 3dB are achieved. The transmission characteristic can be tuned electro-optically at a rate of 2.5 nm/V.