Fermentation is one of methods of food preservation. Plaa-som is a traditional fermented food product.  There are some major ingredients, including freshwater fish, salt, cooked rice and garlic, then are mixed and left to fomentation for 5-7 days in sealed container. This research aimed to study Plaa-som production by mixing of two lactic acid bacteria (LAB) strains Lactobacillus plantarum TISTR 543 and Lactobacillus fermentum TISTR 055 with ratio 1:1 and 2 percent additional. The results of the productions of Plaa-som were made from four various kinds of freshwater fish cultured in Kanchanaburi Province including Nile Tilapia, Jullien's golden-price carp, Smith's barb and Silver barb to the changes of pH value and LAB level were observed. The results showed that the analyzed parameters from four Plaa-som samples such as chemical properties and Lactic acid bacteria level had the similar trend during 6 days of fermentation period. There was decreased a pH value, while the percent titratable acidity (lactic acid) and Lactic acid bacteria (LAB) increased.  After 6 days of fermentation, the products showed pH value lower than 4.50, the percent titratable acidity (lactic acid) higher than 1.65 percent and LAB number about 8.0 log cfu/g.  Additionally, Plaa-som products were produced by four different kinds of freshwater fish had the microbial quality according to the Thai Community Product Standard (CPS 26/2014).