To provide a technology capable of promoting growth of Bifidobacterium bacteria and lactic acid bacteria under an environment causing the growth or no change in cell count while suppressing decrease under an environment causing the decrease. Provided is an agent for promoting the growth of, and/or suppressing a decrease in, Bifidobacterium bacteria and/or lactic acid bacteria containing Arthrospira blue-green algae and/or Spirulina blue-green algae as an active ingredient. Also provided is an oral composition including Arthrospira blue-green algae and/or Spirulina blue-green algae together with at least one type of bacteria selected from the group consisting of Bifidobacterium bacteria and lactic acid bacteria. Furthermore provided is a method for promoting growth of Bifidobacterium bacteria and/or lactic acid bacteria and/or suppressing the decrease including a step for allowing at least one type of bacteria selected from the group consisting of Bifidobacterium bacteria and lactic acid bacteria to coexist with Arthrospira blue-green algae and/or Spirulina blue-green algae.
