PhD students’ poor mental health has been increasingly concerning. However, challenges among PhD students studying aboard are understudied. The Educational and Life Transitions (ELT) model postulates that international PhD students are subject to both academic and acculturative stressors; however, relevant research is limited in the Chinese context. We examined mainland Chinese PhD students’ study and living experiences in Hong Kong using a qualitative approach. Through purposive sampling, 37 mainland Chinese PhD students in different disciplines from public-funded universities in Hong Kong were recruited to participate in online focus group interviews (December 2020–February 2021). The interviews were analyzed using the framework analysis method. Ten themes of academic/acculturative stressors were identified. The academic stressors included: (1) high expectations from the supervisors; (2) emphasis on self-discipline as PhD students; (3) peer comparison in academia; (4) difficulties shifting research directions/academic disciplines; (5) uncertainties about future career. The acculturative stressors included: (1) differences in the political environment; (2) language barriers; (3) difficulties living in Hong Kong; (4) limited social interaction with others; (5) local people’s discriminatory behaviors. This study sheds light on the stressors experienced by mainland Chinese PhD students in Hong Kong. To better address those students’ academic and acculturative stressors, cross-cultural training and additional support from supervisors/the university could be provided.