ABSTRACT The aim of this study was to evaluate the absorption-enhancing effect for antihypertensive activity of an angiotensin I-converting enzyme (ACE) inhibitory oligopeptides in spontaneously hypertensive rats (SHR). The oligopeptides OA3, derived from tuna cooking juice, significantly reduced systolic blood pressure (SBP) in SHR at the doses of 0.5, 0.75, and 1.0 g/kg body weight; their efficacies were exhibited in a dose-dependent manner. Emulsification, microencapsulation, and lipophilization were applied to enhance the antihyperten-sive activity of OA3 at the dose of 0.5 g/kg body weight in SHR individually. Lipophilization revealed most effectively by 16 mm Hg in SBP in SHR 4 h after oral administration; the significant different effect lasted more than 6 h. Such efficacy is greater than that from no further treated OA3 with the dose of 1.0 g/kg body weight. Enhancing treatments by using 30% gum Arabic and 30% lecithin exhibited minor effects by 13 and 11 mm Hg, respectively. Results imply that these additional treatments could further enhance and extend the antihyperten-sive effect of OA3 oligopeptides. This suggests that absorption-enhancing treatments improve the bioavailability of oligopeptides to exhibit higher antihypertensive effect. Furthermore, these enhancing effects may be brought about by the changes in cell membrane permeation or the protection of oligopeptides.