Four structurally unique guanidine alkaloids ecliptamines A-D (1-4) and one known analog (5) were isolated from the aerial parts of Eclipta prostrata (Asteraceae). Their structures were elucidated on the basis of spectroscopic analyses and chemical methods. The inhibitory activities of 1, 2 and 5 were assayed with respect to cyclooxygenase-1 (COX-1) and -2 (COX-2). Compound 5 showed moderate inhibitory activities against COX-1 and -2 with IC50 values of 3.0 x 10(-3) M and 8.3 x 10(-4) M, respectively, whereas aspirin as a positive control displayed the IC50 values of 4.2 x 10(-4) M (against COX-1) and 7.1 x 10(-4) M (against COX-2). (C) 2015 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.