頭髮護理產品中常添加半胱胺酸達到修復頭髮的功能，我國目前只對燙髮類產品中的半胱胺酸有含量限制，其餘髮類產品並無規範，人體中半胱胺酸濃度過高容易引發心血管疾病對人體產生危害，使用含半胱胺酸之化粧品時，半胱胺酸可能經由皮膚進入體內，因此了解髮品半胱胺酸含量就有其重要性。本研究目的在於建立半胱胺酸及其衍生物的定量分析方法。本研究針對半胱胺酸及其衍生物（L-Cysteine hydrochloride、Cysteaminium chloride、N-Acetyl-L-cysteine等），藉由離子對試劑（Ion-pair reagent），以高效能液相層析法結合紫外可見光偵測器（High performance liquid chromatography with UV detection）進行分離，測定其在化粧品中之含量。實驗結果顯示使用Macherey-nagel C18ec（250 mm × 4.6 mm，5.0 μm）層析管柱，以乙?（CH3CN）/ 3.5 mM庚烷磺酸鈉鹽之0.1％硫酸溶液＝2/98 (v/v)之混和溶液為移動相，於流速0.8 mL/min，偵測波長210 nm時可得到最佳之分離條件。在此條件下標準品檢量線之線性相關係數均大於0.9994，而樣品添加回收率也在97.66%以上。此外，此方法對分析L-Cysteine hydrochloride、Cysteaminium chloride及N-Acetyl-L-cysteine之偵測極限分別為0.00103 μg/mL、0.00088 μg/mL及0.00168 μg/mL，因此，此分析方法應可以應用於分析市售樣品中半胱胺酸含量。 Cysteine is often added to hair care products to repair hair. At present time, the cysteine level is only regulated for hair perm products in Taiwan. High cysteine level in human body can easily lead to cardiovascular diseases and harm the health. When using cysteine-containing cosmetics, the transdermal absorption of cysteine should not be ignored. Therefore, knowing the cysteine level in cosmetic products became an important issue. For the above reason, this study is aimed to establish a quantitative method for the analysis of cysteine and it’s derivatives.In this study, the contents of cysteine and its derivatives (L-Cysteine hydrochloride, Cysteaminium chloride, N-Acetyl-L-cysteine) in cosmetic products were determined by high performance liquid chromatography combined with UV detection. Experimental results show that the optimal separation condition is using Macherey-nagel C18ec (250 mm*4.6 mm, 5.0 μm) column, the mixture of acetonitrile and 0.1% sulfuric acid in 3.5 mM heptane sodium salt solution (2 / 98；v/v) as the mobile phase at flow rate of 0.8 mL/min and 210 nm as the detection wavelength. The standard calibration curves of cysteine and it’s derivative show the linear regression correlation coefficient were above 0.994 and the spike recovery were above 97.66%. The detection limits of L-Cysteine hydrochloride, Cysteaminium chloride, N-Acetyl-L-cysteine from this methods were 0.00103 μg/mL, 0.00088 μg/mL and 0.00168 μg/mL respectively. Therefore, this method may be available for the analysis of the levels of cysteine and its derivatives in commercial products.