The invention is related to polynucleotide-based anthrax vaccines. In particular, the invention is plasmids operably encoding Bacillus anthracis antigens, in which the naturally-occurring coding regions for the B. anthracis antigens have been modified for improved translation in human or other mammalian cells through codon optimization. In certain embodiments, the coding regions are also modified so as to remove potential N-linked glycosylation sites. B. anthracis antigens which are useful in the invention include, but are not limited to protective antigen (PA), lethal factor (LF), and fragments, variants or derivatives of either of these antigens. The invention is further directed to methods to induce an immune response to B. anthracis in a mammal, for example, a human, comprising delivering a plasmid encoding a codon-optimized B. anthracis antigen as described above. The invention is also directed to pharmaceutical compositions comprising plasmids encoding a codon-optimized B. anthracis antigen as described above, and further comprising adjuvants, excipients, or immune modulators.