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The content and hydrogen isotope ratios of n-alkanes extracted from recent lake surface sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed. Values were compared with n-alkanes in plants from lake drainages, and delta D values of meteoric water, lake water, and mean annual precipitation. The results showed that n-C-23 was predominantly derived from aquatic plants, and n-C-27-n-C-33 from terrestrial higher plants. The average carbon chain length of n-C-27-n-C-33 (ACL(27-33)) was positively correlated with the mean annual precipitation. delta D values of the long-chain n-alkanes n-C-29 and n-C-31 of terrestrial origin (varying between -214 aEuro degrees and -169 aEuro degrees, and -226 aEuro degrees and -185 aEuro degrees, respectively) were inversely correlated with mean annual precipitation; but in accordance with the average annual variations in delta D (OIPC), delta D values of n-C-31 were strongly related to the delta D values of growing season meteoric water (R (2) = 0.74). The large difference between delta D values of n-C-23 of aquatic origin and n-C-31 (an average of about 27 aEuro degrees) demonstrates the enrichment of the lake water delta D compared to precipitation, caused by strong evaporation in the semiarid-arid areas of the southwestern Tibetan Plateau. Average value of (-95 aEuro degrees) is evidently higher than the value observed in European wet regions (-128 aEuro degrees); besides, (about -116 aEuro degrees) is constant along the study transect (SD = 9), which indicates that n-C-31 is a useful proxy for the environment.