Diarrhea is a disease in which bowel movements occurs more than three times in a day, characterized with watery stools. Diarrhea an be accompanied by blood, which is called as dysentery. Based on the onset, it can be acute or chronic. It caused by various types of microorganisms, including bacteria, viruses, parasites, and fungi. It spread occurs through contaminated food and water sources. WHO states that diarrhea is the second highest cause of mortality in children under five years in the world, with a total 525,000 children death in every year. The knowledge about diarrhea is necessary, so the prevention and treatment can be carried out appropriately. The aim of this study was to describe the level of mothers knowledge about diarrhea in children under five years in Cicau Village, Bekasi Regency. This study is a observational descriptive with a cross-sectional design of 113 subjects that was obtained using consecutive non-random sampling. Data were collected by using questionnaire distributed via online. The results show that majority respondents level of knowledge is good at 80 (70.8%), followed by a sufficient level of knowledge at 29 (25.7%), and poor knowledge at 4 (3.5%). Respondents level of knowledge about definition is good at 71 (62,8%), about causes is good at 77 (68,1%), signs and symptoms is good at 94 (83,2%), prevention is good at 50 (44,2%), and treatment is good at 88 (77,9%). As conclusion, the level of mothers knowledge about diarrhea in children under five years in Cicau Village is good. Keywords: Knowledge; diarrhea; children under five years Abstrak Diare adalah penyakit yang ditandai dengan buang air besar lebih dari tiga kali dalam sehari dengan feses berbentuk cair, bila disertai darah maka dinamakan disentri. Berdasarkan onsetnya, diare dapat terjadi secara akut maupun kronis. Diare disebabkan oleh berbagai jenis mikroorganisme diantaranya bakteri, virus, parasit, dan jamur. Penyebarannya terjadi melalui makanan maupun sumber air yang terkontaminasi. WHO menyebutkan bahwa diare merupakan penyebab tertinggi kedua kematian balita di dunia, dengan jumlah sekitar 525.000 balita di setiap tahun. Pemahaman mengenai diare sangat dibutuhkan agar pencegahan serta penanganan dapat dilakukan dengan sesuai. Penelitian ini bertujuan untuk mengetahui gambaran tingkat pengetahuan ibu tentang diare pada balita di Desa Cicau Kabupaten Bekasi. Merupakan penelitian studi deskriptif observasional dengan pendekatan potong lintang kepada 113 responden, sampel diambil secara consecutive non- random sampling. Pengumpulan data menggunakan kuesioner yang disebarkan secara daring. Didapatkan tingkat pengetahuan ibu balita dengan kategori baik sebanyak 80 (70,8%), kategori cukup sebanyak 29 (25,7%), dan kategori kurang sebanyak 4 (3,5%). Tingkat pengetahuan pengertian diare didapatkan baik sebanyak 71 (62,8%), penyebab diare didapatkan baik sebanyak 77 (68,1%), tanda dan gejala didapatkan baik sebanyak 94 (83,2%), pencegahan didapatkan baik sebanyak 50 (44,2%), serta penanganan didapatkan baik sebanyak 88 (77,9%). Kesimpulan yang didapatkan adalah ibu balita di Desa Cicau memiliki tingkat pengetahuan yang baik mengenai diare.