Abstract: A spectrophotometry for the determination of trace copper has been studied in micelle medium of non-ionic surfactant Tween-20. Copper (II) reacts with sodium diethylddthi-ocarbamate in the presence of Tween-20 in a buffer solution of pH 8. 5 to form a brown yellow complex. The apparent molar absorptivity is 1. 35104 L mol-1 cm-1 at 453nm, and it was stable for more than 48h. Beer's law is obeyed in the range of 0~ 60u g Cu(II) per 25mL. The selectivity of the reaction is improved by the addition of EDTA and ammonium citrate as masking agents. The method has been used for the determination of trace copper in plant materials with satisfactory results.