Since ninety percent of the human population in the world are right-handed, many products and facilities are designed for right-handed people. In Indonesia, writing armchair with desktop fixed at the right side is a common product used at tertiary education level, which is uncomfortable for left-handed students because they have to tilt their bodies awkwardly to the right side. Inadequate facilities of left-sided writing armchair in educational institutions are caused by the unknown difference impact on the handwriting performance of left-handed students when using both types of writing armchairs. The purpose of this research is to find out the handwriting performance differences of left-handed students based on biomechanical ergonomic factors. Thirty left-handed university students, aged 18-23 years, participated in this research to conduct 30-minute handwriting experiments using left-sided and right-sided writing armchair. Four measurements parameter used were electromyography (to measure muscle activity objectively), self-perceived soreness (to measure muscle activity subjectively), writing speed (to measure handwriting efficiency), and posture evaluation index (to measure body posture). The results showed that left-handed students significantly performed better handwriting performance on left-sided writing armchair in all four measurements. When using the right-sided writing armchair, there was pain felt in the upper body. Therefore, it is highly recommended for educational institutions to provide special writing armchair for left-handed students that is accessible and flexible to be used.