Oomycetes are a lineage of absorptive heterotrophic protists within the SAR supergroup of eukaryotes that possess similar morphologies and lifestyles to the fungi. Phytophthora is an economically important oomycete genus that is pathogenic to plants. The cryptochrome photolyase family of proteins includes (6-4) photolyases, blue light-activated enzymes that repair DNA following damage by ultraviolet light. This work reports a multiplication in the number of distinct (6-4) photolyase genes in the plant pathogenic oomycetes that is unique when compared to other SAR species and plant pathogenic fungi. The amino acid sequences of oomycete and fungal (6-4) photolyases display phylogenetic signal. A model of (6-4) photolyase evolution within the oomycete lineage is proposed, which includes two gene duplications within the order Peronosporales. Potential roles played by the increased number of genes coding for (6-4) photolyases among plant pathogenic oomycetes are considered.