Herein we report the first directed evolution of a metal(loid) reductase that changes its substrate specificity. We began with GRLMR, whose preferred substrate is selenodiglutathione. A library of DNA mutants encoding the enzyme was created by error prone polymerase chain reaction (PCR). The library was expressed in E. coli and screened for isolates that survive in otherwise lethal concentrations of SeO3 2-. An evolved enzyme was isolated, in which the substrate selectivity for SeO3 2-was greatly increased as measured by catalytic efficiency (kcat/Km). There was a corresponding decrease in the catalytic efficiency of GS-Se-SG reduction. In addition, the parent enzyme had no measurable activity towards SeO4 2-(selenate), while the evolved enzyme could reduce selenate. Overall, this suggests that substrate selectivity of metal-reducing enzymes can be altered using laboratory directed evolution methods. Notably the enzyme now acts on Se in 3 different coordination environments (GS-Se-SG, SeO3 2-, and SeO4 2-). In light of the findings that metal(loid) reductases can be evolved to act on a diverse range of metal(loid) coordination complexes (as opposed to free ions), the door is opened towards developing enzymes capable of acting on more dramatic ranges of inorganic coordination compound substrates -such as those with different metal(loid) centers.