Phytoglycogen is a naturally occurring glucose-based polymer that has promising applications in personal care, nutrition, and biomedicine. Gold nanoparticles were generated using two-step laser ablation in pure Milli-Q water (AuNP) and Milli-Q containing phytoglycogen (AuNP-Phg) and characterized for size, shape, and nanoparticle concentration. AuNP showed a unimodal distribution of diameters, peaked at 8.8 nm, but AuNP-Phg showed a bimodal distribution: smaller particles, peaked at 4.1 nm, had their growth limited by phytoglycogen; and larger particles, peaked at 7.9 nm, grew unhindered. AuNP, AuNP-Phg and AuNP mixed with phytoglycogen (AuNP+Phg) were used to catalyze the reduction of 4-nitrophenol using the Langmuir-Hinshelwood model. The dispersions had similar k, K_NP and K_BH4; however, the average surface-normalized apparent rate constant was smaller and the induction period was larger for AuNP+Phg compared to AuNP and AuNP-Phg. This suggests that phytoglycogen associates with the gold nanoparticles, preventing the reagent from reaching the catalytic site.