The aim of this research was to determine the effect of amount of metformin HCl on the characteristics (morphology, particle size, drug loading, entrapment efficiency, and yield) of metformin HCl-Ca alginate microspheres using gelation ionotropic method with aerosolization technique. The amount of metformin added was of 0.5 g; 1 g; 1.5 g; and 2 g into 2 g of alginate and 2.5 g CaCl₂ at stirring speed 1000 rpm 30 minutes. Results showed that metformin HCl content for F1, F2, F3 and F4 were 5.09% ± 0.19; 9.61% ± 0.94; 13.11% ± 1.39 and 15.09% ± 0.49 while entrapment efficiency of metformin HCl for F1, F2, F3 and F4 were 48.35% ± 1.11; 41.99% ±1.71; 38.67% ± 2.96 and 30.53% ± 5.37. Respectively yield percentage were 80.92% ± 1.78; 74.12% ± 2.24; 68.27% ± 6.78 and 59.11% ± 9.77. Based on statistic analysis, it was found that there were significantly differences between four formulas. The particle size of formulas decreased by increasing amount of drug. Result of size was 1.82 μm (F1); 1.96 μm (F2); 2.1 μm (F3) and 2,97 μm (F4). It can be concluded that particle size of microspheres increased by increasing amount of metformin HCl and it was found significant differences of metformin HCl content in the microspheres, entrapment efficiency and of yield.