Objective: To investigate the outbreak of mumps in a remote village school of Zhaoqing City, to evaluate and vaccine effectiveness ( VE ) of mumps containing vaccine (MuCV), so as to provide reference for the formulation of epidemic prevention and control strategies. Methods: Through on site case investigations and interviews, case data and epidemic related epidemiological information were obtained. Descriptive and retrospective cohort studies were used to analyze the epidemic characteristics, explore risk factors, and evaluate the protective effect of vaccines. Results: Totally 166 cases of mumps were found, and all of them were students. The total attack rate was 7.79% and the outbreak lasted for 60 days. The first case occurred on October 11th and the last case occurred on December 9th in 2018. Most of the cases aged from 10 to 13 years old, accounting for 66.27%. There were 96 male patients and 70 female patients, with no statistically significant sex difference in the incidence rate ( χ 2=2.40, P >0.05). Involving 28 classes, 11 of which had an incidence rate more than 10%, mainly distributed in grades 2, 4 and 6. There were statistically significant differences in incidence rates among different grades ( χ 2=96.89, P <0.01) and different floors ( χ 2=67.35, P < 0.01 ), with the third floor higher than the other floors. Twelve out of 58 boarding pupils were cases, and boarding pupils were 1.89 times higher in risk of contracting mumps than day students ( RR=1.89, 95%CI =1.10-3.23). Pupils without being given the shot of MuCV were higher in the infection rate than those having the shot ( χ 2=5.70, P <0.05), and the VE % was 35% (95% CI = 7%- 55%). The VE % of one dose was 34% (4%-54%), while the effectiveness of protection was declined with time ( χ 2 trend =6.53, P < 0.05). The effectiveness of vaccine almost diasappeared six years after the shot ( χ 2=1.12, P >0.05). Conclusion Delayed case report and isolation, low rate of receiving MuCV, and decreasing effectiveness of one shot MuCV are closely assocaited with the outbreak and ongoing spread of the epidemic.