This study was carried out to prepare the depolymerized alginates by physical treatment processing with organic acids. The applied physical treatment methods were autoclaving, microwaving, and ultrasonicating, Among several physical depolymerization methods, autoclaving treatment was the most effective for hydrolyzing the alginate to low molecular compounds such as oligosaccharides. Citrate was most effective catalyst in hydrolyzing alginate to some oligosaccharides among organic acids. An acceptable autoclaving conditions for hydrolyzing alginate to oligosaccharides were to treat at $110^{circ}C$ for 90 min and $120^{circ}C$ for 60 min, respectively. The maximum depolymerization percentage produced by autoclaving was $56.8\%$. The depolymerized alginates prepared by autoclaving at $110^{circ}C;and;120^{circ}C$ has oligosaccharides of $3~4 $and $7~8$ species, respectively. The optimum condition for alginate oligosaccarides was autoclaving treatment with $0.5\%$ citrate solution at $120^{circ}C$ for 90 min.