Reproductive protein genes often undergo rapid evolution via a process known as adaptive evolution by receiving more positive selection than the average gene. The molecular evolution of sperm has become of distinct interest to evolutionary biologists due to the immense morphological diversity of sperm cells across taxa. Lepidopteran insects present a compelling model to investigate sperm evolution and diversity, because of their unique, dichotomous spermatogenesis in which they produce a fertilizing component (eupyrene sperm) and an incompetent sperm morph (apyrene sperm). We investigated the evolutionary rates of sperm protein genes of both sperm types in Danaus butterflies. Knowing the ratio of nonsynonymous substitutions to synonymous substitutions of a gene provides insight into the rate of protein evolution relative to DNA evolution. We calculated pairwise dN/dS ratios for all orthologous genes using genome assemblies from either Danaus gilippus or Danaus chrysippus with reference to the Danaus plexippus genome assemblies. We then used the apyrene and eupyrene sperm proteomes of D. plexippus to compare dN/dS ratios of the sperm protein genes to the genomic average. We found no significant difference in neither the dN/dS ratios between sperm proteins and the genomic average, nor the dN/dS ratios amongst the different sperm types in Danaus butterflies. Our results suggest that sperm proteins do not evolve rapidly in the same fashion that other reproductive proteins do. Further exploration into more taxa will be necessary to better understand the molecular evolution of sperm proteins in Lepidopteran insects.