Purpose: This study aimed to investigate the effect of using a keratin solution as a pretreatment agent on damaged hair.Methods: The solution was applied differently with 50% and 100% keratin. Hair tensile strength, absorbance using methylene blue, and gloss were measured, and analysis was performed after scanning electron microscope photographing to determine the effect on damaged hair.Results: Tensile strength, absorbance, and gloss measurement results showed that the average values increased, decreased, and increased for all samples applied rather than for damaged hair, respectively; the statistical results showed a significant difference. By analyzing the cuticle image, the condition was found to be better than that of the control group.Conclusion: The tensile strength, absorbance, gloss, and hair skin analysis of the specimens applied with keratin solution showed differences, which affected the damaged hair.