Eichhornia crassipes (E. C.) is a special aquatic plant, which exhibits excellent tolerance to heavy metals and can be used for the large scale removal of heavy metals from waste water. Here the E. C was used to capture Cd2+, then as an in situ bio-template to successfully synthesize photoelectric CdS microcrystals. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and fluorescence spectrometer. The results indicated that the peanut-like microcrystals with a length of 1.5-1.8 mu m were oriented along (002) plane. The main organic groups in E. C including hydroxyl, primary amide and carboxylate played inducing and controlling roles during the formation of CdS microcrystals in the solution. The PL spectrum showed an emission peak at 450 nm and indicated that the product may have applications in an electronic light device. This approach provided an inspiration on the post-processing of the secondary pollution.