ABSTRAK Penelitian ini bertujuan untuk mengetahui pengaruh ekstrak saponin biji putat air (Barringtonia racemosa) terhadap mortalitas Cerithidea cingulata. Penelitian dilakukan pada bulan November sampai Januari 2014 di Laboratorium Kimia Laut, Jurusan Ilmu Kelautan, Fakultas Kelautan dan Perikanan, dan Laboratorium Kimia, Fakultas Keguruan dan Ilmu Pendidikan, Universitas Syiah Kuala. Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) dengan enam perlakuan konsentrasi (0, 20, 40, 60, 80, dan 100 ppm) dan empat kali ulangan. Penelitian ini menggunakan organisme uji C. cingulata. Data hasil pengamatan mortalitas organisme uji dianalisis dengan program Trimmed Spearman Karber (TSK) versi 1,5. Hasil penelitian menunjukkan bahwa nilai LC50 ekstrak saponin B. racemosa terhadap C. cingulata adalah 35,99 ppm (batas bawah sebesar 22,05 ppm, batas atas sebesar 58,72 ppm). Kata kunci: Cerithidea cingulata, Barringtonia racemosa, Saponin ABSTRACT This research aimed to find out the influence of saponins extract of Barringtonia racemosa kernel on the mortality of Cerithidea cingulata. The research was conducted on November till January of 2014 in the Marine Chemistry Laboratory, the Department of Marine Science, Faculty of Marine and Fisheries, and Chemistry Laboratory, Teacher Training and Education Faculty, Syiah Kuala University. This research used a completely randomized design (CRD) with six concentrations treatment (0, 20, 40, 60, 80, and 100 ppm) and four trials. This research used the C. cingulata as tested organisme. The data of the organism mortality were analysed with a program of Trimmed Spearman Karber (TSK) version 1.5. The research result showed that the LC50 value of saponin extract of B. racemosa kernel on the C. cingulata was 35.99 ppm (lower limit at 22.05 ppm and upper limit at 58.72 ppm). Key words: Cerithidea cingulata, Barringtonia racemosa, Saponin