Objective To study the blood zinc level and activity of T lymphocyte in children with attention deficit hyperactivity disorder (ADHD),and to promote the therapy of ADHD. Methods Blood zinc levels of 60 ADHD patients and 50 healthy controls were detected by atomic absorption spectrometry,at the same time,the T lymphocyte subsets of CD3⁺,CD4⁺ and CD8⁺ in peripheral blood of the two groups were measured by flow cytometer. Results The blood zinc level was lower in ADHD children [(73.24±9.89) μmol/L] than that in health controls [(82.51±7.81) μmol/L,t=5.373,P<0.01].Levels of CD3⁺、CD4⁺、CD4⁺/CD8⁺ T lymphocyte subsets in ADHD group[(57.9±5.0)%,(26.8±3.9)%,1.059±0.234],had significantly depressed,as compared with those of healthy controls[(68.2±4.9)%,(36.5±4.7)%,1.432±0.279,t=10.84,11.85,7.63,P<0.01].Level of CD8⁺ had no difference between the two groups.Correlation analysis showed that the blood zinc level was positively correlated with level of CD4⁺ and CD3⁺ T lymphocyte (r=0.577,0.411,P<0.01). Conclusion The blood zinc level decreased significantly,the balance of T lymphocyte subsets was disorder,and the decrease of CD4⁺ T lymphocyte was the most evident in ADHD children.Addition of zinc can make for the therapy of ADHD.