Penelitian ini dilakukan untuk mengetahui efek toksisitas akut berbagai konsentrasi ekstrak air daun sernai yang diberikan secara peroral dengan satu kali pemberian pada mencit (Mus musculus). Penelitian ini menggunakan rancangan acak lengkap (RAL) dengan 5 perlakuan dan 3 ulangan. Kelompok kontrol negatif (P0) diberi akuades, kelompok P1, P2, P3, dan P4 berturut turut diberi ekstrak air daun sernai dengan konsentrasi 20%, 30%, 40%, dan 60%. Efek toksik pemberian konsentrasi ekstrak air daun sernai secara klinis ditentukan berdasarkan kriteria Loomis. Hasil penelitian menunjukkan bahwa ekstrak air daun sernai dengan konsentrasi 20%, 30%, 40%, dan 60% tidak menunjukkan adanya ketoksikan dan kematian pada mencit. Disimpulkan potensi ketoksikan akut sediaan uji ekstrak air daun sernai termasuk dalam kategori praktis tidak toksik.(This study was aimed to determine acute toxicity effect of various concentrations of sernai leaves water extract which administered once orally in mice (Mus musculus). Completely Randomized Design (CDR) was used in this study with 5 treatment groups and 3 repetitions. As a negative control (T0), were only given aquadest, while the treatment groups of I (T1), II (T2), III (T3), and IV (T4) were given sernai leaves water extract with concentrations of 20%, 30%, 40% and 60% respectively. Identification toxic effects of sernai leaves water extract were determined based on Loomis criteria. The results showed that sernai leaves water extract with 20%, 30%, 40%, and 60% concentrations did not show any toxicity and death in mice. It was concluded that acute toxicity potential of sernai leaves water extract including practically non-toxic class.)