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Objective To investigate the safety of normal saline isolation zone in laser, radiofrequency and microwave thyroid ablation. Methods Fifteen pigs were divided into laser, radiofrequency and microwave three groups. Ten mL sterile normal saline were injected postanesthesialy to separate thyroid from surrounding tissues and form a liquid isolation zone with the width >5 mm. Two of 3 temperature measurement needles were placed in the tissues beneath 5 mm, 10 mm from ablation needle, and one needle in normal saline isolation zone 5 mm from ablation needle other side. Porcine thyroid was ablated using ultrasound-guided laser, radiofrequency or microwave respectively and a thermal ablated lesion in thyroid was formed with inner diameter about 10 mm. Two-dimensional ablation process was observed and recorded by ultrasound in real time and the change in temperature of ablation was carefully observed and recorded by temperature measurement needle. Results There were no significant differences statistically in the volume of ablation lesion and the volume of defect measured by perfusion after thermal ablation among laser, radiofrequency or microwave (P>0.05). Ablation process was proved effective by laser, radiofrequency or microwave ablation with the temperature at 5 mm from center point. The temperature in normal saline isolation zone of three pigs with microwave ablation exceeded 60.0 ℃, and up to 80.7 ℃ in one pig. Conclusions Normal saline may provide safe isolation zone in thyroid thermal ablation for laser or radiofrequency ablation, but not appropriate for microwave ablation. We recommended to use non-polar substances with great difference in dielectric properties from surrounding biological tissues as isolation zone, which can improve safety for microwave thermal ablation.