It is found that the fluorescence intensity of morin-Al(3+) complex can be greatly enhanced by proteins in the presence of cetyltrimethylammonium bromide (CTAB). It is considered that protein and CTAB provide a hydrophobic environment with low polarity and large viscosity, resulting in the fluorescence enhancement of morin-Al(3+) complex. The experiments indicate that under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins (such as bovine serum albumin (BSA), human serum albumin (HSA) and egg albumin (EA)) in the wide range, and their detection limits (S/N=3) are 2.6 x 10(-9), 1.4 x 10(-8) and 1.6 x 10(-8) g ml(-1), respectively. This method has satisfactorily been used for the determination of protein in actual sample. In comparison with most of fluorimetric methods reported, this method is quick and simple, and has high sensitivity, wide linear range and good stability.