This study examines secondary traumatic stress (STS), burnout and compassion satisfaction (CS) in Flemish foster care workers (FCW) during the COVID-19 lockdown. Even though child welfare workers are at increased risk for STS and burnout, these constructs have not been studied in FCW so far. Additionally, the COVID-19 measures severely impacted Flemish FCW’s work, personal and client environment, possibly stimulating the onset of STS and burnout and weakening CS. Moreover, this study aims to identify the work, client and personal factors determining high levels of STS and burnout and low levels of CS among FCW during the lockdown. STS, burnout and CS levels from 434 Flemish FCW were inquired with the Professional Quality of Life Scale. Low mean levels of STS and moderate mean levels of burnout and CS were reported during the lockdown. FCW who experienced a negative impact of COVID-19 measures on their work, had a high amount of worrisome placements due to birth parents in their caseload and low emotional stability are an at-risk group for both STS and burnout during the lockdown. CS was strongly determined by the impact of the COVID-19 measures on work and personality traits. Emotional stability determined the three outcome variables, making this a key characteristics for FCW during the lockdown. Consequently, during adverse circumstances, foster care agencies should pay extra attention and offer additional support to those FCW they estimate emotionally less stable and who struggle with the birth parents in their caseload.