Abstract: The in vitro release characteristics of gentamicin sulfate pulybutylcyanoacrylate nanoparticles were studled using a dialysis system comprising dialysis bag and receptor chamber. The whole apparatus was placed in a water bath shaker thermostated at 37℃,and shaken at 50 cpm. The concentration of gentamicin in the receptor chamber was periodically determined by first derivative spectrometry.The results showed that the in vitro release of gentamicin sulfate from polybutylcyanoacrylate nanoparticles is characteristically biphasic,with an initial fast release(the burst effect),followed by a much slower release. These release profiles can be well modelled using a biexponential function. The related parameters of release kinetics have been calculated according to the blexponential function,and some factors that may affect the release characteristics were studied.