The effects of surfactants on the formation of chitosan nanoparticles were studied. The high, medium and low molecular weight chitosan (Mv~10[superscript 6], 1.5x10[superscript 5] and 10[superscript 4]) were mixed with the evaluated surfactants in micellar system under different mixing techniques : stirring, ultrasonicating and vortexing. Only the aniomic surfactants, sodium bis(ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulfate (SDS) allowed the formation of chitosan nanoparticles in aqueous media. At the chitosan concentration of 2.5 mM the formation of nanoparticle was observed when the mole ratio of surfactant/chitosan was higher than 14:1 and 20:1 for AOT and SDS, respectively. The size and zeta potentials of the particles determined by photo correlation spectroscopy and zetasizer were 110+-10 nm and -47.42 +- 5 mV, respectively. The chitosan/AOT nanoparticles obtained can be loaded with tetracycline at AOT/chitosan/tetracycline mole raio of 20:1:1 with 50% entrapment efficiency. The suspensions of the chitosan/AOT nanoparticles were stable at ambient condition for at least 30 days.