Abstract: Changes in organic acid contents and their relationship with relevant enzyme activities in nectarine fruits “Chaohongzhu” were studied. Results show that nectarine fruit total acid content hits a peak 49 days after full blossom and then gradually declines during later fruit development stages. Malic acid has similar change pattern as total acids, but citric acid gradually increases in content during fruit development with little reduction in the ripening stage of the fruit. Analysis on the activities of organic acids in relation to relevant enzymes shows no relation between citrate synthase activity (CS) and citric acid content. Increase in the activity of malic enzyme (ME) in the late period of nectarine fruit development accelerates degradation of malic acid in fruits. There is a significant correlation between malate dehydrogenase(MDH) activity and fruit malic acid content. This shows that nectarine fruit organic acid content can be reduced by MDH activity inhibition and enhancement of ME activity. This can equally increase the sugar to acid ratio of nectarine fruits.