Strategies used by Microcystis aeruginosa, bloom-forming cyanobacteria, for potential inorganic arsenic (arsenate and arsenite) uptake, and depuration kinetics under phosphate-enriched (+P) and depleted (-P) treatments were examined via short- and long-term experiments. Phosphate depletion improved arsenate or arsenite uptake rate constants. M. aeruginosa arsenite influx occurred considerably faster than arsenate influx under +P or -P treatments. Different phosphate regimes yielded significant impacts on long-term but not on short-term arsenic (As) uptake. In addition, considerable differences were observed in short-term As efflux between live and dead cells after arsenate or arsenite pre-exposure. Arsenic depuration rates in live M. aeruginosa cells were affected not only by accumulation rates of different As inorganic species but also by phosphate concentrations in tested media, which was inferred from estimated kinetic parameters. Specifically, +P was clearly found to inhibit As efflux after live M. aeruginosa cells were pre-exposed to As(V). Efflux was higher for dead cells no matter the inorganic As species involved. Owing to higher As uptake and depuration rates under -P treatments, P deficiency will considerably accelerate As uptake and efflux processes in aquatic environments.