Stimuli-polymer brushes are found all over the world around us in different forms and show progressive changes from the 15th century to the 21st century.Especially, thermo-responsive polymer brushes(PNIPAM) have so many applications and show interesting improvements in developing qualitative, smart & highly performing polymer brushes. The name of polymers is given to be brush because a surface coating consists of polymer tethered to a surface. There are a number of parameters that can affect the swelling capacity of the polymer brushes (PNIPAMs). Some of them are temperature, cross-link density, molecular weight, ion concentration, pHvalue and others. This project work focused on reviewing the definitions, the properties, the methods of synthesis, and the effects of cross-link density & molecular weight on the swelling ratio of thermo-responsive polymer brushes.Thermo-responsive polymer brushes have lower critical solution temperature(LCST) and upper critical solution temperature (UCST) properties as well they can be synthesized or prepared in three types of techniques. These are physio-adsorption, “grafting-to” and “grafting-from” methods.Selectively, the project work emphasized on two broad ideas. First, as the temperature increases, the brush thickness (H) of thethermo-responsive polymer brush decreases. Since cross-link density is directly proportional with the temperature, the cross-link density increases when the temperature of the brush increases andas a result the swelling ratio decreases and vice versa up to the LCST for good solvents. Secondly,when the temperature of thethermo-responsive polymer brush increases or decreases the water content in the brush decreases and increases respectively. Increasing or decreasingthe water content of the polymer can increase or decrease the swelling capacity of the polymer brushes respectively. So that increasing the molecular weight, increases the swelling ratio of the PNIPAM polymer brush and decreasing the molecular weight decreases the swelling ratio of the thermo-responsive polymer brushup to the LCST for good solvents.