Poly(galactaramidoamine) (PGAA) is a cationic co-polymer of dimethyl-meso-galactarate and pentaethylenehexamine. PGAA electrostatically complexes with plasmid DNA (pDNA) to form nano-sized particles. In this study, we show that PGAA-pDNA polyplexes generate high transfection efficiencies in human embryonic kidney (HEK293) and murine macrophage-like (RAW264.7) cell lines. PGAA-pDNA mediated transfection is a function of the amine:phosphate (N/P) ratio at which the polyplexes are prepared. The maximum expression of luciferase was obtained using polyplexes prepared at an N/P ratio of 40. Polyplexes prepared at increasing N/P ratios did not significantly increase in size but did result in decreasing luciferase expression. Cellular toxicity increased as the N/P ratios at which the polyplexes were prepared increased.