<p><b>OBJECTIVE</b>To study the epidemiological and clinical features of the mycoplasma pneumoniae pneumonia (MPP) that occurred in a single class of a kindergarten in Beijing in July 2006.</p><p><b>METHODS</b>The environment and the attendance record of the kindergarten from the beginning of August 2005 to the end of July 2006 were investigated, and the sick status of the children absent for illness were interviewed by face to face or telephone through their parents. The disease data of the in-patient children with MPP were collected through questionnaires and analyzed. Serological screening for MP was performed with the Serodia Myco II gelatin particle agglutination test (Fujirebio, Japan).</p><p><b>RESULTS</b>In mid-July 2006, in a day-care kindergarten with 3 grade classes, 3 out of 25 six-year-old children in the top class were hospitalized within 4 days and diagnosed as MPP. A total of 8 children had the symptoms of fever and cough during late May and mid-July in 2006, 5 children conduct chest radiographs and all had pneumonia, all these five children showed antibody positive for MP, 3 of them showed a more than 4-fold increase in antibody titer to MP in serum. There were no pneumoniae cases in the other two classes during the same period, and no pneumoniae cases happened among the teachers in the top class and the parents of the 5 pneumoniae children. All the children were moved to this classroom temporarily with limited ventilation and sunshine in March 2006. After improvement of the ventilation in the classroom, no additional pneumoniae cases occurred in the top class till the early September 2006. The 5 MPP children showed neither sneeze and nasal obstruction, nor skin rash, earache and any other extrapulmonary complication, and their peripheral white blood cell count was in the normal range (3.9 - 7.7) x 10(9).</p><p><b>CONCLUSION</b>The MPP outbreak in a kindergarten was caused by poor ventilation of the temporary classroom. MP infection in children is liable to cause pneumonia.</p>