A novel method for the determination of trace rhodium by laser thermal lens spectrometry（LTLS） based on the sensitive color reaction between rhodium（Ⅲ） and 2-（5-bromo-2-pyridylazo）-5-dimethylaminoaniline（5-Br-PADMA）was established.The experiment results showed that in a media of pH 3.6-6.0 HAc-NaAc buffer solution,rhodium（Ⅲ） can react with 5-Br-PADMA to form a violet-red complex.The complex can be changed into another green-blue proton species possessing a high abosorption characteristics in 1.2 mol/L HClO4.The optimal concentrations of HClO4,HCl,H2SO4 or H3PO4 were found to be 0.6-3.6 mol?L-1 for HClO4,0.6-3.0 mol/L for HCl,1.2-4.0 mol/L for H2SO4 and 1.8-4.5 mol/L for H3PO4,respectively.The maximum absorption wavelength was 612 nm which matched well with the output wavelength（632.8 nm） of He-Ne laser.The analytical curve was linear in the concentration range of 5-140 μg/L for rhodium,and the detection limit was 1.1 μg/L.The method,having high sensitivity and good selectivity,was applied in the determination of trace rhodium in the rhodium-carbon catalyst with satisfactory results.