<![CDATA[Escherichia coli is a Gram-negative bacterium that can cause various infections in humans, while increasing antibiotic resistance has encouraged the search for natural antibacterial sources. This study aimed to analyze the antibacterial activity of ethanolic extract of peacock flower (Caesalpinia pulcherrima) leaves against Escherichia coli and identify its secondary metabolites. A laboratory-based in vitro experimental study was conducted using the disc diffusion method. The ethanolic extract was tested at concentrations of 75%, 100%, 125%, and 150%, with chloramphenicol as the positive control and sterile distilled water as the negative control. Phytochemical screening revealed the presence of tannins, flavonoids, saponins, and steroids, while alkaloids were not detected. All extract concentrations produced inhibition zones against E. coli, measuring 13.13, 13.26, 13.98, and 15.98 mm, respectively. The largest inhibition zone was observed at 150%, whereas chloramphenicol produced a zone of 32.78 mm. One-Way ANOVA indicated a significant difference among groups (p < 0.001). The findings demonstrate that the ethanolic extract of C. pulcherrima leaves exhibits antibacterial activity against E. coli, with greater activity at higher concentrations, although its inhibitory effect remains lower than that of chloramphenicol. ABSTRAK Escherichia coli merupakan bakteri Gram-negatif yang dapat menyebabkan berbagai infeksi pada manusia, sementara peningkatan resistensi antibiotik mendorong pencarian sumber antibakteri alami. Penelitian ini bertujuan menganalisis aktivitas antibakteri ekstrak etanol daun kembang merak (Caesalpinia pulcherrima) terhadap Escherichia coli serta mengidentifikasi kandungan metabolit sekundernya. Penelitian menggunakan metode eksperimen laboratorium secara in vitro dengan metode difusi cakram. Ekstrak etanol daun kembang merak diuji pada konsentrasi 75%, 100%, 125%, dan 150%, dengan kloramfenikol sebagai kontrol positif dan akuades steril sebagai kontrol negatif. Skrining fitokimia menunjukkan adanya tanin, flavonoid, saponin, dan steroid, sedangkan alkaloid tidak terdeteksi. Seluruh konsentrasi ekstrak menghasilkan zona hambat terhadap E. coli, masing-masing sebesar 13,13; 13,26; 13,98; dan 15,98 mm. Diameter zona hambat terbesar diperoleh pada konsentrasi 150%, sedangkan kloramfenikol menghasilkan 32,78 mm. Analisis One-Way ANOVA menunjukkan adanya perbedaan signifikan antar kelompok (p < 0,001). Hasil penelitian menunjukkan bahwa ekstrak etanol daun kembang merak memiliki aktivitas antibakteri terhadap E. coli, dengan aktivitas meningkat pada konsentrasi yang lebih tinggi, meskipun masih lebih rendah dibandingkan kloramfenikol.]]>
