The present study was focused on the simultaneous removal of Ni (II) and Co (II) ions from aqueous solutions by ultrasound-assisted adsorption onto carboxylated nanoporous graphene (G-COOH). Nanoporous graphene was synthesized by chemical vapor deposition method then functionalized by carboxyl groups and finally characterized using SEM, XRD, EDX, BET and FT-IR techniques. The effects of variables such as pH, sonication time, adsorbent dosage, and temperature on simultaneous removal of Ni (II) and Co (II) ions were studied and optimized. The kinetic and isotherm experiment data could be well described with the pseudo-second order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity of G-COOH for Ni (II) and Co (II) ions was 94.34 mg g-1 and 87.72 mg g-1, respectively. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic in nature.