AbstractIt is well known that the Camellia japonica leaf exhibits antioxidant activity because of its high content of polyphenolic compounds. Thus, the extract prepared from mature leaves of C. japonica (CJML) has been widely used as an anti‐ageing material in foods and cosmetics. Concerning the process of growing C. japonica, it is expected that the extract from green leaves (CJGL) has superior effects compared with that from mature leaves. However, there are few reports that discuss the difference between green and mature leaves. In this study, both CJML and CJGL were extracted with 50% 1,3‐butylene glycol (1,3‐BG) and used for investigations. In a chemical examination, we compared both extracts in terms of scavenging activities against hydrogen peroxide (H2O2) and hydroxyl radicals. CJGL exhibited higher scavenging activities against both types of ROSs compared with CJML. In addition, CJGL reduced the carbonylation of tape‐stripped stratum corneum (SC) after UVB irradiation. In a biological study, the intra‐cellular ROS level of HaCaT keratinocytes precultured with CJGL for 24 h was significantly lower than that of the control cells. Furthermore, cell damage induced by H2O2 exposure was attenuated by 24 h precultivation with CJGL but not by 2 h precultivation. The results of examinations indicate that CJGL possess properties that reduce oxidative stress. In addition, the result of 2 h precultivation with CJGL suggests that CJGL might affect the status of intra‐cellular antioxidants.