Objective: This study examines the effects of a well-being intervention based on the PROSPER (i.e., Positivity, Relationship, Outcomes, Strength, Purpose, Engagement, and Resilience) framework, on well-being outcomes among preschool in-service teachers in Hong Kong during the COVID-19 pandemic.Method: We recruited 76 in-service teachers (Mage=26.05, SD=4.71, nfemale=93.4%). Participants completed a survey that measured the PROSPER components of well-being in baseline and 2-month after baseline, from February 2021 to May 2021. They were randomly assigned into the intervention group (n=36; who received four intervention workshops, an online activity and four educational videos with self-reflection activity) and waitlist control group (n=40; who received four intervention workshops after completing the data collection). MANCOVA and ANCOVA, controlling for sex, age and teaching experience, were adopted to examine the intervention effects.Results: MANCOVA results showed a significant multivariate group x time interaction effect of the intervention on the PROSPER outcome variables compared to the control group, Wilks’ Lambda F(7,65) =3.80, p<.001, η2=.29. Results of univariate analyses suggested that participants in the intervention group scored significantly higher on positivity, strength, purpose, and resilience (η2=.08-.11, p<.05) than those in the control condition over time.Conclusion: Our findings provide preliminary evidence on the mental health benefits of the PROSPER-based psychological intervention program among in-service preschool teachers. School principals are encouraged to invest in school-based teacher training initiatives that focus on teachers’ well-being as pandemic-related job stressors might potentially deplete their psychological resources and mental health. Copyright © 2022 European Conference on Education.