Online teaching became an alternative approach for the teacher to run the teachinglearning activities during the COVID-19 pandemic. In this context, this study aimed to identify the issues of mathematics teachers in teaching mathematics through online mode during the pandemic where issues represented the problems and challenges. Altogether 415 mathematics teachers from different levels participated in this crosssectional survey. A self-constructed tool consisting of six categories of problems as Skills and training related problems (STP), learner related problems (LRP), course management and evaluation related problems (CMERP), resource using skills and infrastructure related problems (RUSIP), teaching related problem (TRP), and support and collaboration related problem (SCP) was employed in the study. T-test, ANOVA, correlation, and multiple linear regression were the major statistical techniques used to analyze the data. The findings indicate that the technical skills and digital resources with the learners and teaching figures and curves were major challenges of mathematics teachers in online mode of instruction. Additionally, gender, number of available devices, institute types, teaching levels, ICT training, and types of job were explanatory factors to determine the challenges of mathematics teachers in online teaching during the pandemic.