INTRODUCTION: The effect of power and duration of ultrasonic irradiation on the synthesis of thiazoles via the Hantzsch reaction was investigated. METHODS: The reaction of phenacyl bromides with thioamides under ultrasonic irradiation afforded the target thiazoles in good yields. RESULTS: The results showed that high power and long irradiation time cause the decomposition of the reaction materials, and for this reaction, the irradiation power of 720 watts and a total duration of 4 minutes, wherein a pulsing function was performed in 50% of each second, were considered the most suitable irradiation properties for the synthesis of thiazoles through the Hantzsch reaction. CONCLUSION: The use of mild conditions, short time frame, high yields, simple separation of the reaction product, and no use of the base for neutralization are the advantages of the present method.