Soyghurt was a probiotic drink made by adding a lactic acid food (LAB) into the soy milk. In general, cultures used was Lactobacillus bulgaricus and Streptococcus thermophilus. This study used L. plantarum cultivated from soybean solid waste so it was assumed to have good growth so as to produce good quality soyghurt. The aim of this research was to get the best fermentation time for microbiological quality of soyghurt using L. plantarum IDY L-20. This research was conducted experimentally using Randomized Complete Design with four treatments and four replications. The treatments in this study were P1, P2, P3, and P4; each treatment was fermentation time 8 hours, 16 hours, 24 hours, and 32 hours. The results showed that fermentation time had significant effect (P <0,05) on pH, viscosity, total acid, total BAL, and total sugar. The best treatment for making soyghurt using L. plantarum IDY L-20 was P3 (24-hour fermentation length) with pH (4,14), viscosity (996 cP), total acid (0,88%), total LAB (11,00 log cfu/ml), and total sugar (4,37%). The longer time fermentation used will decrease the pH and total sugar while the viscosity, total acid, and total LAB value will increase. This was because of LAB continues to perform metabolic processes.