The traditional product, named "Mam chua ca sac" or "Mam tieu xuong", is a sour fermented soft bone fish (Trichogaster trichopterus , Trichogaster microlepis). Fish was mixed with salt, sugar, ethanol, powder grilled rice, garlic, chilli and naturally fermented at 28-30^oC within a span of 20-30 days. Fermented products had the harmonious combination of sweet, sour,and salty taste; especially, still remianed the whole shape of fish but their skeleton turned very soft that it seems boneless in the sense of taste. Investigating the factors affecting to the soft bone process indicated that the bone was soaked in organic acid solution (lactic acid, acetic acid) at pH 4 during 72 hours, the calcium dissolved into soaking solution but the whole bone frame still remained and made fish bone soft. Also, the same result was obtained when fish bone was soaked in MRS broth medium (inoculated with isolated lactic acid and bacteria Pediococcus acidilactici, Lactobacillus farciminis at pH 4-pH 5; then, sterilized at 121^oC for 15 minutes) in a periods of 72 hours soaking hours, 40-60% of calcium dissolved into solution. After this stage, a small amount of calcium spread out and the change of calcium percentage in fish bone was not significant. As the result, fish bone became soft and the whole bone frame remained in the medium of pH less than 5.