In this work, long-period waveguide grating-based tunable wavelength filters using organic-inorganic grafting poly(methyl methacrylate) (PMMA) materials are designed and fabricated by metal-cladding directly defined technique. The thermal stabilities and optical properties of the organic-inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 dB and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/ • C and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.