ABSTRACT Perennial sow-thistle (Sonchus arvensis L.) has been traditionally used as a medicinal plant. It contains secondary metabolites with several functions mainly as antioxidant, and its ability to dissolve kidney stones. It is expected that proper harvest time could increase leaf production and secondary metabolites, especially flavonoids. This study aimed at determining harvest time and flavonoid production of Perennial Sow-thistle. The research was conducted in July 2015 to December 2015 at IPB Organic Farm Cikarawang, Dramaga, Bogor. This study used randomized block design with single factor namely harvest time and 3 replications. There were 4 harvest time treatments i.e. (1) leaves harvested gradually i.e. basal leaves at vegetative then upper leaves harvested at early generative stage, (2) leaves harvested gradually i.e. basal leaves at vegetative then upper leaves harvested at maximum generative stage, (3) basal leaves harvested together with upper leaves at early generative stage, and (4) basal leaves harvested together with upper leaves at maximum generative stage. The result showed that basal leaves were harvested at vegetative stage then stem leaves harvested at maximum generative stage produced the highest fresh weight of upper leaves. Total flavonoids content were found the highest in upper leaf when basal leaves harvested together with the upper leaves at budding and flowering. Keywords: leaf area, luteolin, nutrient content, organic ABSTRAKTempuyung (Sonchus arvensis L.) secara tradisional telah digunakan sebagai tumbuhan obat. Tempuyung mengandung metabolit sekunder dengan beberapa fungsi utama yaitu sebagai antioksidan dan peluruh batu ginjal. Diharapkan pengaruh waktu panen dapat meningkatkan produksi daun dan kandungan metabolit sekunder terutama flavonoid. Tujuan penelitian ini untuk menentukan waktu panen dan produksi flavonoid tempuyung. Penelitian ini telah dilaksanakan pada bulan Juli sampai Desember 2015 di kebun percobaan IPB Cikarawang, Dramaga, Bogor. Penelitian ini menggunakan rancangan acak kelompok lengkap faktor tunggal yaitu waktu panen. Terdapat 4 perlakuan yang diulang sebanyak 3 kali yaitu: (1) panen daun secara bertahap (daun bawah saat vegetatif) dan kemudian daun atas dipanen saat terbentuk kuncup bunga, (2) panen daun secara bertahap (daun bawah saat vegetatif) dan kemudian daun atas dipanen setelah bunga mekar, (3) panen daun bawah bersamaan dengan daun atas saat terbentuk kuncup bunga, dan (4) panen daun bawah bersamaan dengan daun atas setelah bunga mekar. Hasil penelitian menunjukkan panen daun bawah secara bertahap dan kemudian panen daun atas setelah bunga mekar menghasilkan bobot basah daun atas tertinggi. Panen daun secara bersamaan menghasilkan kadar flavonoid total daun atas tertinggi.Kata kunci: kadar hara, luas daun, luteolin, organik