This research was conducted to determine the effect of adding the extract of butterfly pea flower (Clitoria ternatea L.) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus on the quality of yogurt. This study used a factorial Completely Randomized Design with two factors, i.e the addition of butterfly pea extract (I = 4% 8% 12%) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus (A = 1:1 1:2 2:1). The results obtained showed that the addition of butterfly pea flower extract had a highly significant effect on the pH value, total acid, antioxidant activity, total lactic acid bacteria, viscosity, total soluble solid , color value, color hedonic and general acceptance hedonic. Ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus had a highly significant effect on the pH value and total acid, had a significant effect on antioxidant activity, viscosity and total soluble solid. The interaction between the two factors had a significant effect on the total acid value of yogurt. Yoghurt with the best quality was addition of butterfly pea extract 12% (I3) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilu 2:1 (A3). It was based on the parameters of antioxidant, total lactic acid bacteria, color value, and organoleptic.This research was conducted to determine the effect of adding the extract of butterfly pea flower (Clitoria ternatea L.) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus on the quality of yogurt. This study used a factorial Completely Randomized Design with two factors, i.e the addition of butterfly pea extract (I = 4% 8% 12%) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus (A = 1:1 1:2 2:1). The results obtained showed that the addition of butterfly pea flower extract had a highly significant effect on the pH value, total acid, antioxidant activity, total lactic acid bacteria, viscosity, total soluble solid , color value, color hedonic and general acceptance hedonic. Ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilus had a highly significant effect on the pH value and total acid, had a significant effect on antioxidant activity, viscosity and total soluble solid. The interaction between the two factors had a significant effect on the total acid value of yogurt. Yoghurt with the best quality was addition of butterfly pea extract 12% (I3) and the ratio of starter Lactobacillus bulgaricus and Streptococcus thermophilu 2:1 (A3). It was based on the parameters of antioxidant, total lactic acid bacteria, color value, and organoleptic.