The　interaction　of　procaine　hydrochloride　and　β-cyclodextrin　in　aqueous　solution　was　studied　using　resonance　Rayleigh　scattering　technology.　The　molar　ratio　of　the　inclusion　complex　was　1:1　established　by　spectrophotometry.　The　resonance　Rayleigh　scattering　technology　was　first　applied　in　the　determination　of　the　β-cyclodextrin　inclusion　constant.　The　inclusion　constant　of　procaine　hydrochloride-β-cyclodextrin　complex　Kf　is　1.23　×　102　and　1.27　×　102　l　mol-1　for　method　I　and　1.15　×　102　and　1.21　×　102　l　mol-1　for　method　II.　These　determination　results　were　in　correspondence　with　the　results　of　the　spectrophotometric　and　fluorescence　methods.　Therefore,　the　resonance　Rayleigh　scattering　method　can　be　used　as　a　new　technology　for　the　determination　of　the　inclusion　constant.　©　2002　Elsevier　Science　Ireland　Ltd.　All　rights　reserved.