Oxygen isotope analysis was carried out, by use of a new method (oxalate equilibration method) of preparing CO(2) for mass spectrometry, on water samples extracted from a number of biological samples collected in Misasa Town and Hashizu Coast, Tottori Prefecture. The δ values (the per mil enrichment of (18)O in sample waters relative to the Standard Mean Ocean Water) were suggested to be distributed in the living things as follows. The water absorbed by plant roots was supposed to have the same δ value with the water outside it (δs. about -8‰), and in a rapidly transpiring plant, this water reached the leaves, partly infiltrating into the phloem. When transpiration was slow, on the other hand, the isotopic composition of ascending xylem sap was modified by the exchange of water with phloem. where leaf water with a higher δ value was migrating. As Gonfiantini et aI. (1965) and Dongmann et al. (1972) have odserved, leaf waters were enriched markedly in (18)O in the daytime. A criterion of the δ of leaf water may be the sum of δs and △δ that corresponds to the (18)O fractionation factor in the H(2)O(I)-H(2)O(v) system. The sum comes to about 0‰ at ordinary leaf temperatures. and really δ values near 0‰ were observed in leaves of some herbaceous plants, in exudate from a tip of vine of Kudzu, in body fluid of herbivorous insects, etc., but higher δs (up to +19‰) were also observed in some other leaves such as pine needles, Especially leaves showed an increase in δ by about 10 ‰ toward the pnd of November when the average temperature fell below 10℃, probably because of accumulation of the daily enrichment as a resul t of slow water absorption and circulation. A few plant species grown on a dune were analyzed and it seemed that, among them, herbaceous plants were dependent on spraied sea water and pine trees on ground water. δ's of petal water were dispersed (-9～-3‰), probably according to the volume-to-transpirational flux ratio of water in the petals. Succurent fruits in enlarging stage seemed to have lower δ's near δs, but in maturing stagp δ's increaspd to about -4‰, i.e., to the avpraged δ of Ieaf water in the day and night. Herbivorous insects (imagines and la rvae) in general had distinctly higher δ values than carnivorous insects, the border being at -1‰. However, lower δ's at about -5‰ were obserbed on aphides which might have been sucking somewhat dilutpd leaf water from seave tube cells. Sometimes the δ of a herbivorous insect was a few per mil higher than that of the leaf it was nibbling, probably as a result of evaporation of water from the insect and of respiration. The level at about -3‰ common for carnivorous insects could not be explained, although tipula and chironomus making a swarm also showed a δ value on the level. Blood of a heron did not show such a low δ as supposed from its food habit. As compared with the drinking water of -8‰, blood and urine were found to have an identical δ in the range of -4 to -5‰ in either mouse or man, The δ value of the oxidation water produced in man's body was estimated to be about -6‰ from an approximate water balance.