Abstract: Objective: To detect the proportion of natural killer T(NKT) cells(CD3⁺ CD16⁺ CD56⁺) in peripheral blood among healthy adults by flow cytometry.Methods: The whole peripheral blood of 141 healthy adults and 30 patients with lung cancer were collected and stained with double colored fluorescent antibodies,followed by lysing red blood cells and washing cells.The percentages of NKT cells,T lymphocytes and T cell subsets were measured and analyzed by flow cytometry.The 95% reference range was calculated by percentile.Results: The average of percentage NKT(CD3⁺ CD16⁺ CD56⁺) cells in the 141 healthy adults' peripheral blood was 4.16%;95% reference range by percentile was from 0.78% to 11.71%.The averages of NKT cells in the age groups of 18-30-year,31-50-year and 51-70-year were 4.64%,3.91%,and 3.57%,respectively.There was no significant difference among the three groups(P>0.05).The average percentage of NKT cells in the peripheral blood of patients with lung cancer did not change significantly,compared to the normal group.In addition,the proportions of T cell subsets and NK cells measured in this study were within the normal ranges of clinical reference.Conclusions: The reference range of 95% of the NKT cells(CD3⁺ CD16⁺ CD56⁺) in normal adults' peripheral blood is 0.78% to 11.71%,with an average and median of 4.16% and 2.97%,respectively.Although NKT cells decrease with the rise of age,there is no linear correlation between them.No significant difference in NKT cell proportions is observed between the lung cancer patients and the normal group.