This is the first to present evidence of agarolytic activity in strain from genus Stenotrophomonas. We purified an extracellular β-agarase from marine bacterium Stenotrophomonas sp. NTa. This alkaline agarase exhibited stricking stability across a wide pH range. It also had a relatively good resistance against some detected inhibitors, detergents and urea denaturant. We identified the enzymatic hydrolysates and their antioxidant activities.