Magnesium oxide modified diatomite waste (MgO-DW) was successfully synthesized. The adsorption behaviors of methylene blue (MB) and acid orange (AO) over MgO-DW were studied. The samples involved were characterized by Fourier transform infrared, scanning electron microscopy, energy dispersive spectrometer, Brunauer Emmett Teller, X-ray diffraction, and zero point of charge analyses. Experimental factors including contact time, adsorbent dosage, pH, and initial dye concentration were explored. Maximum adsorption capacity of MgO-DW for MB (pH 11.0) and AO (pH 2.0) was 25.02 and 35.13 mg/g at 303 K, respectively. The results showed that Langmuir isotherm and pseudo-first-order kinetic models fitted the experimental data better. Regeneration tests confirmed that MgO-DW has promising potential in reusability.