Cheese starters, Streptococcus thermophillus, lactobacillus delbrueckii ssp bulgaricus, lactobacillus helveticus that used in the manufacture of cheese, were subjected to ultrasound in the range 0, 5, 10, 15 and 20 min at 20 KHZ frequency and amplitude of 80% at 20°C and pH= 7. Inactivation total viable counts and cell lysis release of lactate dehydrogenase, enzyme (LDH) due to autolysis of lactic acid bacteria were examined during the subsequent cheese ripening. Results showed that the lactococci were more sensitive than the lactobacilli to ultrasound up to 20 min (3-5) log cycle reduction and others were more reduction tolerant against lethal effect of ultrasound. The degree of inactivation of starters was found to be affected of ultrasound exposure time, starters were treated with a longer exposure time, showed a greater reduction in numbers and had less out-growth of starters during ripening also release of LDH and thus autolysis, was increase in cheese when using ultrasound up to 15min in both 1-day-old and 1-month-old of hard cheese samples.

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