Abstrak. Penelitian ini bertujuan untuk mengetahui pengaruh perlakuan konsentrasi minyak cengkeh untuk mengendalikan patogen terbawa benih pada benih tomat secara in vitro dan in vivo. Penelitian ini dilaksanakan pada bulan Agustus sampai dengan November 2017 di Laboratorium Ilmu dan Teknologi Benih Fakultas Pertanian Universitas Syiah Kuala. Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) pola faktorial yang terdiri dari dua faktor. Faktor yang petama yaitu konsentrasi minyak cengkeh (C) yang terdiri atas 6 taraf yaitu 0,000%, 0,010%, 0,015%, 0,020%, 0,025%, 0,030%. Faktor kedua adalah jenis patogen (P) yang terdiri dari 2 taraf yaitu Fusarium oxysporum dan Pythium sp. Dengan demikian terdapat 12 kombinasi perlakuan dengan 3 kali ulangan, sehingga didapatkan 36 satuan percobaan. Adapun parameter in vitro yang diamati adalah diameter koloni dan daya hambat patogen lalu parameter in vivo yang diamati adalah pre emergence damping off, post emergence damping off, keparahan penyakit dan tinggi tanaman tomat. Hasil penelitian menujukkan konsentrasi minyak cengkeh perpengaruh terhadap diameter koloni, daya hambat patogen, pre emergence damping off, post emergence damping off, keparahan penyakit dan tinggi tanaman tomat. Perbedaan jenis patogen yang digunakan berpengaruh terhadap diameter koloni, daya hambat patogen, keparahan penyakit dan tinggi tanaman, namun tidak berpengaruh nyata terhadap persentase pre emergence damping off dan persentase post emergence damping off. Konsentrasi minyak cengkeh yang terbaik untuk mengendalikan patogen terbawa benih baik secara in vitro maupun in vivo adalah 0,020%. Jenis patogen yang lebih dapat dikendalikan secara in vitro adalah F. oxysporum dan jenis patogen yang lebih dapat dikendalikan secara in vivo adalah Phytium sp.The Effectiveness Clove Oil to Control Seed Borne Pathogens In Vitro and In Vivo on Tomato Seeds (Lycopersicum esculentum)Abstrack. This study aims to determine the effect of clove oil concentration treatment to control seed borne pathogens on tomato seeds in vitro and in vivo. The research was conducted from August until November 2017 at the Technology and Seed Science Laboratory, Faculty of Agriculture, Syiah Kuala University. The design used was Completely Randomized Design (RAL) factorial pattern consisting of two factors. The first factor is the concentration of clove oil (C) which consists of 6 levels, that were 0.000%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%. The second factor is the type of pathogen (P) which consists of 2 levels, that were Fusarium oxysporum and Pythium sp. There were 12 combinations of treatments with 3 replicated, so that obtained 36 units experiment. The in vitro observed variables were diameter of the colony, pathogen inhibitory activity and in vivo observed variables were pre emergence damping off, post emergence damping off, disease severity and tomato plants height. The results showed that the concentration of clove oil had a significant effect on diameter of the colony, pathogen inhibitory activity, pre emergence damping off, post emergence damping off, disease severity and tomato plants height. The difference type of pathogen had a significant effect on the diameter of the colony, pathogen inhibition, disease severity and tomato plant height, but had no significant effect on the percentage of pre emergence damping off and the percentage of post emergence damping off. The best concentration of clove oil to control seed borne pathogens both in vitro and in vivo is 0.020%. The type of pathogen that can be more controlled in vitro is F. oxysporum and the type of pathogen that can be more controlled in vivo is Phytium sp.