Objective: An epidemiological investigation was carried out in school X in Jinan, Shandong Province, China, to identify the cause, epidemiology, and etiological characteristics of a febrile respiratory disease outbreak; and therefore to control the dissemination. Methods: Both field epidemiological investigations and laboratory examinations were carried out. Results: Forty cases were identified, in which 38 cases were students and two were teachers. Clinical manifestations included fever, coughing, headache, and sore throat. A total of 21 pharyngeal swab specimens were collected and 18 tested positive for adenovirus. The adenovirus hexon gene was sequenced in three of the 18 positive specimens and the results showed a 100% homology with the standard HAdV-55 HEXO. Conclusions: The outbreak originated from an adenovirus-infected student, who spread the pathogen to her classmates and teacher. The teacher then further disseminated the disease within the school which led to 40 febrile respiratory infections.