Mycoplasma synoviae can cause worldwide respiratory diseases, synovitis, or subclinical symptoms in poultry. M. synoviae infection occurs throughout the yr and causes significant economic losses, including increased mortality, condemnations, medication, and live production cost. In the present study, the seroprevalence of M. synoviae among 44,395 non-vaccinated chickens from 21 provinces in China from 2010 to 2015 was estimated using ELISA. The overall seroprevalence was 41.19%. Seropositive rates in different yr ranged between 24.70 and 57.20%; the highest seropositive rate was observed in 2010, and the lowest was observed in 2013. The prevalence rates varied greatly in different provinces from 5.10 to 100%. Of the 463 commercial flocks tested, 375 (80.99%) were positive for M. synoviae by ELISA. The seasonal distribution ranged between 26.83% (in October) and 53.98% (in July). An investigation of chickens according to age further showed that M. synoviae can infect chickens at any age. Our findings indicate that M. synoviae infection is very common in China and should prompt further research into its prevalence to develop effective control and prevention strategies.