Studies have shown that international students are at increased risk of experiencing poor mental health. The COVID-19 pandemic has had further negative impacts on the psychological well-being of students. In this quasi-experimental study, we examined the impact of a brief acceptance and commitment therapy (ACT) -based group intervention delivered by videoconference (ACT videoconference; n = 48). We used an equivalent in-person group intervention administrated prior to the pandemic as a reference group (ACT face-to-face; n = 53). In addition, we investigated the exposure – response relationship, dropout attrition, acceptability, and user experiences. International university students participated in five online group meetings using a videoconferencing app during the COVID-19 pandemic and were compared with students participating in five face-to-face group meetings prior to the pandemic. Symptoms (stress, anxiety, depression) and process measures (psychological inflexibility, mindfulness, engaged living) indicated similar positive changes in both groups (e.g. PSS-10, ACT videoconference dw = 0.54; ACT face-to face dw = 0.94; AFQ-Y, ACT videoconference dw = 0.55; ACT face-to-face, dw = 0.84), with a slightly larger effect in the ACT face-to-face group. This study suggests that brief ACT-based group workshops can be effective in enhancing the psychological flexibility of international university students, and decreasing symptoms of stress, depression and anxiety whether delivered by videoconference or face-to-face format.