in the present work, a simple and sensitive method was developed for determination of morphine and heroin using gold nanoparticles as resonance rayleigh scattering (rrs) and colorimetric technique’s probe. synthesized gold nanoparticles by sodium citrate reduction method have a negative charge layer on their surfaces because of self-assembled citrate anions on their surface. binding of morphine and heroin to gold nanoparticles results in the aggregation of gold nanoparticles, which leads to the enhancement of the rrs signals. the rrs intensities were measured using a common spectrofluorometer by the synchronous scanning at ??=0 nm. also the aggregation changes color of gold nanoparticles to blue. the degree of blue to red color changes quantitatively by increasing these drugs concentrations, this change of color makes it’s colorimetric detection possible. absorbance of different concentrations measured at the 623nm by uv-vis spectrophotometer. the linear range for rrs method is 0.03-0.3 ?gml-1 for morphine and 0.01-0.1 ?gml-1 for heroin and the corresponding detection limits are 12 ngml-1 and 1.13 ngml-1. the linear range for spectrophotometry method is 0.03-0.3 ?gml-1 for morphine and 0.01-0. 1 ?gml-1 for heroin and the corresponding detection limits are 12 ngml-1 and 3.4 ngml-1. the proposed method were applied to determination of morphine and heroin in some bioilogical samples.