The adsorption behavior and mechanism of amino-crosslinked hypromellose (AHM) adsorbent crosslinked with epichlorohydrin and modified with diethylenetriamine were studied. This material is unprecedented, and the modification method used to obtain it is relatively simple. The parameters affecting the adsorption of methyl orange (MO) dye by AHM such as pH, adsorbent dosage, contact time, initial concentration, and temperature were investigated. The experimental results show that the optimal adsorption time and dosage were 30 min and 3.6 g L-1, respectively. It was found that the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model provide a good description of the adsorption process, indicating that the adsorption of MO by AHM is mainly controlled by the chemical bonding interactions. Analysis of the thermodynamic parameters showed that the process of MO adsorption on AHM is spontaneous and endothermic. The morphology, surface chemical bonding, crystal structure, specific surface area, and temperature stability of AHM were characterized by SEM, FTIR, XRD, BET, and TGA measurements. The results showed that the AHM materials had large pores, which is favorable for adsorption. AHM may also have an increased content of amino-functional groups that are beneficial for adsorption. The maximum MO adsorption capacities of AHM were 15.56 mg g(-1), whereas the maximum adsorption capacity of the unmodified hypromellose was 2.12 mg g(-1). It is important to note that the adsorption efficiency of AHM remained above 62% after five adsorption-desorption experiments. Therefore, AHM can be used as an efficient and environmentally friendly adsorbent material for the removal of MO from water.