This study tried to explore what motivates international students to attain PhD graduation requirements in mathematics and sciences studies in a Chinese research university. The design of the study was qualitative and all collected data were analyzed by thematic analysis. The study explored the motive forces that enable international PhD students to persist and solve all challenging situations to fulfill PhD graduation requirements in mathematics and sciences studies. The internal and external motivations were found to be the main cause of their persistence to continue their studies until they meet their graduation requirements. International PhD students in mathematics and sciences reported to be challenged by the communication barriers, unfit social interaction, advanced software to be used and different high requirements to be attained in a research university. The discussions of findings considered other existing related studies and theories that help people to persist and achieve their desired goals and targets. Possible solutions to existing challenges and further research’ areas were suggested in this study.