Abstract: Objective To understand the antibody level to pandemic influenza A (H1N1) virus and analyze the infection status in population in Shandong. Methods A total of 1617 serum specimens were collected from outpatients and blood donors at 10 January, 25 January, 20 February and 20 March in 2010, the serum antibody to pandemic influenza A (H1N1) virus was detected by hemagglutination-inhibition (HI) test. Results The 4 surveys indicated that antibody positive rate and GMT were 18.24% and 13.86, 26.95% and 16.65, 30.33% and 17.74, 11.53% and 12.72 respectively; The antibody positive rates in 4 age groups were 26.88% (0-5 years old), 30.72% (6-17 years old), 19.03% (18-55 years old) and 10.38% (56 years old). Conclusion The antibody level to pandemic influenza A (H1N1) virus in some population in Shangdong increased steadily, but it had not reached protective level. The highest antibody positive rate (30.33%) and GMT (17.74) were detected in February in 2010, and the antibody positive rate was highest in age group of 6-17 years old.