The king oyster mushroom (Pleurotus eryngii) is an edible mushroom with high nutritional and medicinal value; large fruiting body, attractive shape, firm and thick flesh, and a slight crunch. This study was conducted to select lactic acid bacteria (LAB) strains that are capable of fermenting and determine suitable conditions for fermenting king oyster mushrooms. Ten LAB strains were selected, and the experimental conditions included incubation temperature (room temperature, 30 °C, and 37 °C), bacterial density (103, 105, and 107) cells/g, kinds of glutinous rice (Thai sticky rice, Thai fragrant sticky rice, Long An sticky rice, Cai hoa vang sticky rice, brown sticky rice), mushroom-to-sticky rice ratio (40:60, 50:50, and 60:40 w/w), and salt concentration (1 %, 2 %, and 3 % w/w). The results showed that HCGT31 strain had the highest lactic acid production after 2 days of fermentation(19.05 g/L). The optimal fermentation conditions for king oyster mushrooms were at 37 °C and an inoculum density of 107 cells/g, using Thai fragrant sticky rice with a ratio of mushroom and glutinous rice of 50:50 w/w and 1 % w/w salt concentration. The product after 24 h of fermentation had an acid content of 7.43 g/L, a pH of a 4.44, and a total sensory evaluation score of 15.89/20 according to TCVN3215:79.