Microwave radiation was used for synthesis of an adsorbent using rice husk. The activation of the rice husk sample was performed by H3PO4 and 6min of the microwave radiation with power 700W. The synthesized adsorbent was characterized by SEM, FT-IR, BET and XRD techniques. These analyses showed the prepared adsorbent is an amorphous and mesoporous nano-adsorbent with BET surface area 276.43m2/g. It has some aromatic groups and O-H, C=C, C.O and C=O bands in its structure. Adsorption of alizarin yellow on the synthesized nano-adsorbent was investigated and the influences of adsorbent dosage (0.1-2 g/L) and temperature (25-40 °C) on dye removal from aqueous solution were investigated. The kinetic, equilibrium and thermodynamics studies of alizarin yellow removal from aqueous solution using the prepared adsorbent were carried out. The adsorption performance of alizarin yellow on the prepared adsorbent was compared with a commercial activated carbon. The importance of this study is in providing a condition for preparation of a low cost adsorbent with high adsorption capacity (712.63 mg/g) for alizarin yellow. The comparison of adsorption capacities of the prepared adsorbent from rice husk and other adsorbents proved it is a perfect adsorbent.