Nanoclays have become an important material in several industries such as paint and coating industry, cosmetics, paper, water treatment, nanocomposite production and pharmaceutical industries. In recent years, much attention has been paid to the preparation of nanoparticles for purification of water. In this research, the application of nanoclay as a strong absorbent for the removal of tetracycline has been investigated. Tetracycline, as one of the most dangerous biological contaminants, has attracted many researchers in recent years. The complex structure of tetracycline and the irreparable damage of this drug to the environment exacerbate the need for a strong, practical, yet inexpensive absorbent to eliminate this contaminant. Clay soils, including Montmorillonite, due to Features such as cation exchange capacity, high specificity, low cost, inflation and chemical deficiency are known as a potential absorbent in the biodegradation industry. In the present study, nanoclay was firstly purified by montmorillonite to obtain maximum absorbance and then modified by several methods. Activated montemorillonite by 0.25 CEC surfactant had the highest removal rate of tetracycline. . It was also observed that with increasing the activation temperature, due to the regular arrangement of surfactants between the montmorillonite layers, the absorption capacity of the montmorillonite increased significantly. Absorption kinetics experiments were conducted to investigate the structure and nature of tetracycline adsorption on montmorillonite as adsorbent. For all adsorbents, the process of absorbing at an earlier stage was at a higher rate and, after a certain period of time, reached at the highest amount of adsorption. In the next step, the pseudo-second-order model was fitted to the results. It was observed that the montmorillonite which was activated by the 0.25 CEC surfactant had the highest absorption efficiency. The second kinetic model fitted to the kinetic results was an intraparticle diffusion model. It was observed that all samples had three linear regions. The first linear region had a very high kinetic rate indicating that tetracycline was absorbed on the outer surfaces of the montmorillonite. In the second linear step, tetracycline particles began to penetrate the layers of montmorillonite and diffusion occurred. In the third linear region decreased significantly and became almost zero. The X-ray diffraction analysis indicates an increase in the space between the montmorillonite layers after absorption. In fact, this confirms the absorption of tetracycline particles between the layers of montmorillonite. Also, the X-ray diffraction analysis showed that the surface distances of montmorillonite by surfactants have increased the intervals of all adsorbent layers. All experiments indicate that by adding excessive modifier, the amount of absorption capacity decreased, which could be due to clogging of the surfaces and edges of the montmorillonite by surfactants. In the next step, the maximum amount of tetracycline absorption on montmorillonite samples was obtained using absorbance isotherm tests of 310 mg / g of adsorbent. In the end, the effect of environmental pH on the tetracycline absorption mechanism by montmorillonite was investigated, which showed that absorbent and absorbable isoelectric points play the most role in the absorption process. Thus, at pH less than 3, tetracycline has a cationic form, resulting in a maximum absorption. The results showed that montmorillonite had a maximum absorption capacity of 350 mg /g absorbent at pH= 2.5