By the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the molecular weight and quantity of protein are determined. After the electrophoresis, gel is stained by coomassie brilliant blue (CBB) or other chemicals. The quantity of protein is determined by densitometry. In the low quantity below a few hundred nano grams of protein, the signal intensity is proportional to the quantity. By the increment of the quantity, the signal increment is suppressed. In the present report, the adequate standard curve function was determined, where the protein contents ranged from 0.020 to 10 μg.