Solar ultraviolet (UV) radiation has a great influence on green organisms, especially plankton like Chlamydomonas. A human metallothionein-2 gene, which is generally considered to have an anti-radiation function by its coding product, was transferred into the chloroplast genome of Chlamydomonas reinhardtii.To dynamically measure the UV effects on Chlamydomonas cells grown in liquid tris-acetate-phosphate medium, a new method was developed based on the relationship between the chlorophyll content of an algal culture and its absorbance at 570 nm after the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. In this experiment, both the wild-type and the transplastomic C. reinhardtii cells were cultivated in 96-well microplates containing liquid tris-acetate-phosphate medium in the absence or presence of zinc, copper,cadmium and cysteine. The transgenic C. reinhardtii showed a higher resistance than wild-type to UV-B exposure under all the examined conditions. Metals in the medium had positive impacts on both types of cells,but had significant influence only on the transplastomic cells. However, the high cell viability of the transgenic alga at the end of the 8 h UV-B treatment disappeared after a 20-h recovery culture. Cysteine did not protect cells from UV-B damage, but clearly enhanced the growth of both wild-type and transgenic C.reinhardtii.