Objective: To investigate the epidemiological characteristics of a pertussis outbreak in a primary school in Rizhao City, so as to provide reference for the prevention and control strategy of pertussis. Methods: The method of field epidemiological investigation was used to determine case definition for case search and case investigation,and the characteristics of the outbreak were comprehensively analyzed through descriptive epidemiological method. Results: The outbreak lasted for 29 days from April 19 to May 17, 2022, with a total of 14 cases detected. All the cases were students aged 6-7 years from Class 2, Grade 1 in this primary school,including 6 boys and 8 girls. The attack rates of boys and girls were 30.00% and 34.78%, respectively. The time interval from onset to diagnosis of 14 cases ranged from 2 to 22 days, with a median of 10 days. All of them had received 4 doses of Diphtheria and Tetanus and acellular Pertussis(DTaP) combined vaccine, and the interval between the last vaccination and the onset of disease was 5-6 years. After isolated treatment, all the 14 sick students recovered, without severe or death cases. Conclusion The outbreak of pertussis in a primary school may be related to the decline in the effectiveness of pertussis vaccine protection over time, the lax implementation of a school registration and reporting system for sick absenteeism, and the poor sensitivity of existing pertussis surveillance systems.