Stimuli-responsive drug delivery system is a concept in which a drug is delivered at a suitable rate in response to stimuli. States of diseases may cause an alteration in some parameters of the body (e.g. in tumors) and the onset and offset of the drug delivery can be done by using this as a stimuli or a "trigger". Stimuli-responsive ("intellectual" or "sharp") resources and molecules show abrupt property changes in response to miniature changes in external stimuli such as pH, temperature etc. For regulated drug delivery, environmental stimuli such as pH and temperature, which undertake phase transition in polymer system, have been investigated. Thermally-responsive polymers can be tuned to a preferred temperature variety by copolymerization with a hydrophilic co-monomer or a hydrophobic co-monomer. Hydrophilic co-monomers increase the LCST while hydrophobic co-monomers decrease the LCST. The stimuli responsive polymer for regulated drug delivery can contain a polymer and copolymers having equilibrium of hydrophilic and hydrophobic groups. A number of these polymers have been investigated extensively and some success in drug delivery with them has been achieved, such as polymers and copolymers of N-isopropylacrylamide, PLGA, and PLA, HEMA etc. Thus this review is designed for stimuli pH and temperature responsive polymeric nanoparticles, which would be helpful to treat various cronic diseases such as cancer and others, for scientists in the field of the regulated drug delivery system.