The effects of the Covid-19 pandemic have penetrated all aspects of human life, including education. One of the pandemic consequences is that universities require that lectures be carried out online, where may affect student learning outcomes. This study aimed at determining the impact of online lectures during the Covid-19 pandemic on the professional competence of students as mathematics pre-service teacher at the Muhammadiyah University of Purworejo. This was quantitative research. The population were the first semester students in 2020 at the Mathematics Education Department of Muhammadiyah University of Purworejo. The research sample was taken through random cluster sampling, including 30 students from the population. The data were obtained using a professional competency test instrument. The data processing method used one-sample average statistical test by comparing with the professional competency scores of students in 2018. Based on the study results, it was found that there was a significant decrease in the professional competency scores of Mathematics Education students whose lectures were conducted online during the Covid-pandemic 19 compared to the professional competency scores of Mathematics Education students whose lectures were conducted face-to-face.