Abstract: Objective To compare the application of HE and enzyme histochemical staining in assessing the viability of hepatocellular carcinoma (HCC) cells coagulated by microwave ablation at different temperatures. Methods Two groups of mice (n=6) with transplanted homogenic HCC were treated by microwave ablation at 60 ℃ and 50 ℃ for 3 min, respectively. Before and after microwave ablation, paraffin sections and frozen sections of the tumors were prepared for routine HE staining and enzyme histochemical staining with nicotinamide adenine dinucleotide diaphorase (NADH-diaphorase), respectively, and observed under microscope. Results Shortly after microwave ablation, the morphology and arrangements of the nucleus of the ablated tumor cells in the two groups showed no obvious alteration in HE stained sections, but in sections with enzyme histochemical staining, the activity of NADH-diaphorase in ablated tumor tissue at 60 ℃ disappeared, suggesting the death of HCC cells; sporadic activity of the enzyme was detected in the coagulated tumor at 50 ℃, indicating tumor cells surviving the ablation. The ablation effect was markedly different between the two groups (P<0.01). Conclusion HE staining is not suitable for evaluation of HCC destruction immediately after microwave ablation, and detection of NADH-diaphorase activity with the enzyme histochemical method better suits this purpose.