We report here the first successful transfer of T-DNA of Agrobacterium tumefaciens carrying the genes coding for β-glucuronidase ( uidA), green fluorescent protein ( gfp) and hygromycin phosphotransferase ( hpt) to the nuclear genome of the green alga Chlamydomonas reinhardtii. The transformation frequency (which was based on hygromycin resistance phenotype) was 50-fold higher than that of the glass bead transformation. Molecular and genetic analyses performed on transformants revealed the stable nuclear integration and expression of transgenes. The simplicity of Agrobacterium-mediated gene transfer and the high transformation frequency as well as the precision of T-DNA integration will enable further molecular dissection of this important model organism to understand basic plant metabolic processes as well as to exploit the system for biotechnological applications.