Penelitian ini bertujuan untuk mengetahui pengaruh konsentrasi probiotik terhadap kepadatan dan komposisi infusoria yang ditumbuhkan pada subtrat daun pisang (Musa paradisiaca). Penelitian ini merupakan penelitian eksperimental Rancangan Acak Lengkap (RAL) satu faktor dengan lima taraf perlakuan yaitu konsentrasi probiotik 0 ml/l, 0,5 ml/l, 1 ml/l, 2 ml/l, dan 4 ml/l dengan pengulangan sebanyak 4 kali untuk setiap perlakuan. Pengamatan dilakukan pada hari ke 2, 4, 6, 8, 10, 12, dan 14 untuk memperoleh data berupa kepadatan infusoria, keanekeragaman spesies infusoria beserta jumlah individu per spesies. Data tersebut digunakan untuk mengetahui kepadatan, indeks keanekaragaman (H’), indeks dominansi, serta komposisi spesies infusoria pada setiap perlakuan. Hasil penelitian menunjukkan bahwa konsentrasi probiotik berpengaruh signifikan terhadap kepadatan insufosia (sig 0,010) berdasarkan analisis One Way ANOVA. Indeks keanekaragaman infusoria termasuk dalam kategori rendah pada semua perlakuan. Sejalan dengan hasil tersebut, indeks dominansi pada semua perlakuan berada dalam kategori tinggi. Hasil penelitian menunjukkan bahwa Paramecium sp mendominasi komposisi infusoria pada semua konsentrasi probiotik. Konsentrasi probiotik sebesar 0,5 ml/l, 1 ml/l memicu pertumbuhan Chlorococcum dan digantikan populasi Trichocerca tenuior pada konsentrasi 2 ml/l dan 4 ml/l. Kata kunci: dominansi, infusoria, keanekaragaman, probiotik Probiotic Concentrations Effect on Density and Compotition of Infusoria Grown on Banana Leaf Substrate ABSTRACT This study aims to determine the effect of probiotic concentration on the density and composition of infusoria grown on banana leaf substrate (Musa paradisiaca). This research is an experimental study in a one-factor Completely Randomized Design (CRD) with five levels of treatment, namely the probiotic concentration 0 ml/l, 0,5 ml/l, 1 ml/l, 2 ml/l and 4 ml/l with 4 repetitions for each treatment. Observations were made on days 2, 4, 6, 8, 10, 12, and 14 to obtain data in the form of infusoria density, infusoria species diversity and the number of individuals per species. These data were used to determine the density, diversity index (H'), dominance index, and the composition of infusoria species in each treatment. The results showed that the concentration of probiotics had a significant effect on the density of insuffocia (sig 0.010) based on One Way ANOVA analysis. The infusoria diversity index was included in the low category in all treatments. In line with these results, the dominance index in all treatments was in the high category. The results showed that Paramecium sp dominated the composition of the infusoria at all concentrations. The probiotic concentration was 0,5ml/l; 1ml/l; stimulated the growth of Chlorococcum and was replaced by Trichocerca tenuior populations at concentrations of 2 ml/l and 4 ml/l. Keywords: dominance, infusoria, diversity, probiotic