An L-amino acid is produced by culturing a bacterium having an L-amino acid-producing ability in a medium containing a processed product of a microalga which promotes production and accumulation of the L-amino acid by the bacterium. The process product is produced by disrupting the culture of the microalga, and/or extracting the culture of the microalga, or fractionating the culture of the microalga or the disrupted culture. The processed product contains a mixture of organic substances produced by the microalga, a hydrolysate of the disrupted microalga culture, and/or an extract or fractionation product of the microalga culture. The processed product can also contain a saccarification product of starch or a hydrolysate of fats and oils. The bacterium is cultured to produce and accumulate the L-amino acid in culture, and the L-amino acid is collected from the culture.