ABSTRAKPupuk organik cair (POC) urin kelinci mempunyai kandungan unsur hara yang baik bagi tanaman. Semangka merupakan salah satu buah yang mempunyai potensi besar untuk dibudidayakan. Penelitian ini bertujuan untuk mengetahui konsentrasi pupuk organik cair urin kelinci yang tepat untuk pertumbuhan dan produksi tanaman semangka, dengan pengurangan pupuk anorganik sebanyak 50%. Penelitian ini dilakukan pada bulan Januari sampai dengan April 2018, di Curug Serpong Tangerang Selatan, pada ketinggian ± 25 meter di atas permukaan laut dengan jenis tanah Latosol. Metode penelitian menggunakan Rancangan Acak Kelompok (RAK) dengan enam perlakuan konsentrasi POC urin dan diulang sebanyak empat kali. Perlakuan terdiri dari pupuk anorganik 100%, pengurangan pupuk anorganik sebesar 50% ditambah POC urin dengan konsentrasi 5, 10, 15, 20 dan 25ml/Liter di aplikasikan sebanyak 250 ml air / tanaman. Parameter yang diamati adalah jumlah daun, jumlah cabang, jumlah bunga jantan, jumlah bunga betina, bobot buah dan diameter buah. Hasil penelitian menunjukkan bahwa penambahan bermacam – macam konsentrasi POC urin kelinci memberikan pengaruh nyata terhadap jumlah daun, jumlah cabang, dan jumlah bunga jantan tanaman semangka tetapi tidak berpengaruh nyata terhadap jumlah bunga betina, diameter buah dan bobot buah semangka. ABSTRACT Liquid organic fertilizer (LOF) rabbit urine has good nutrient content for plants. Watermelon is one of the fruits that has great potential to be cultivated. This study aims to determine the concentration of liquid organic fertilizer of rabbit urine which is appropriate for the growth and product of watermelon plants, with a reduction of inorganic fertilizers by 50%. This research was conducted from January to April 2018, at Curug Serpong, South Tangerang, at an altitude of ± 25 meters above sea level with Latosol soil types. The research method used a Randomized Block Design (RBD) with six treatments for urine LOF concentrations and repeated four times. The treatment consisted of 100% inorganic fertilizer, 50% reduction in inorganic fertilizer plus urine LOF with concentrations of 5, 10, 15, 20 and 25ml / Liter applied as much as 250 ml of water / plant. The parameters observed were the number of leaves, number of branches, number of male flowers, number of female flowers, fruit weight and diameter of fruit. The results showed that the addition of various kinds of rabbit urine LOF concentrations had a significant influence on the number of leaves, number of branches, and the number of male flowers of watermelon plants but did not significantly affect the number of female flowers, fruit diameter and watermelon weight.