The present invention relates to a composition for improving or promoting hair growth, which contains, as an active ingredient, a photosensitizer-peptide conjugate, and to a method for screening for the hair growth promoter using the active ingredients. ALA, which is the photosensitizer of the present invention, is preferably activated by LED radiation, and more preferably activated by radiation having a long wavelength of 650 to 675 nm. The peptide of the present invention is a peptide in which 3 to 7 amino acid residues are incorporated (most preferably, glycine-histidine-lysine), and may cooperate with the photosensitizer to enable very superior hair growth improving or promoting effects using light radiation. Further, the composition of the present invention may exhibit further superior effects when natural extracts (for example, Cimicifuga heracleifolia extracts, Scutellaria baicalensis extracts or Codonopsis lanceolata extracts) are added. Thus, the composition of the present invention can be significantly advantageously applied to drugs, quasi-drugs, and cosmetics.