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To investigate the adsorption performance of different modified hydroxyapatite nanoclusters (nHAs) for oxytetracycline (OTC), amphoteric modification of nHA with 50% and 100% dodecyl dimethyl betaine (BS) was performed to obtain BS-modified nHA (50BS-nHA and 100BS-nHA). Grafting modification of BS-nHA with thiourea–citral (TC) and thiourea–vanillin (TV) was also conducted to acquire TC- and TV-modified BS-nHA (TC-BS-nHA and TV-BS-nHA), respectively. The microscopic morphology of the tested materials was studied by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and specific surface area (SBET) detection. Batch method was used to investigate the adsorption characteristic of OTC on the tested materials, and the effects of pH, temperature, and ionic strength on OTC adsorption were compared. Results were as follows: (1) After amphoteric and grafting modification, the pH, cation exchange capacity (CEC), and SBETof nHA decreased, whereas the total organic carbon (TOC) content increased. SEM and FTIR showed that TC and TV were successfully linked to BS-nHA. (2) The isothermal adsorption curves of each test material for OTC were in accordance with the Langmuir model. The maximum adsorption amount (qm) of OTC ranged from 87.85 to 168.85 mmol/kg, and was in the order of TC-BS-nHA > TV-BS-nHA > BS-nHA > nHA. (3) The OTC adsorption of the test materials was negatively correlated with pH and ionic strength and positively correlated with temperature, and the optimum adsorption conditions were 30°C, pH = 5, and ionic strength of 0.01 mol/L. (4) The results of thermodynamic analysis indicated that the adsorption of OTC was a spontaneous, endothermic, and entropy-increasing reaction. The adsorption of OTC by each tested material conformed to the pseudo-second-order kinetic equation. TOC was the key to determining the adsorption capacity of each test material to OTC.