Research on teacher noticing in the field of mathematics education research has increased in the last decade; however, only a few studies have investigated the social and cultural impact on teachers' noticing. This paper describes results of an international comparative study on (in-service) mathematics teachers' professional noticing in China and Germany, representing Eastern and Western cultures. In this study, 203 teachers in China and 118 teachers in Germany participated in a video-based assessment of their professional noticing, i.e. perception, interpretation, and decision-making competencies. Item response theory (IRT) and differential item functioning (DIF) were employed for data analysis. Findings of the study revealed that German teachers performed significantly better than Chinese teachers on noticing aspects related to general pedagogy; in contrast, Chinese teachers outperformed their German counterparts on noticing aspects connected to mathematics instruction. Further DIF detection analysis found that German mathematics teachers demonstrated particular strengths in "perception" as a sub-facet of noticing; in contrast, Chinese teachers tended to demonstrate strength in "analyzing and decision making" as other sub-facets of noticing. These findings suggest that societal and cultural factors, such as different philosophical paradigms, traditions of teacher education, and teaching and mathematics curriculum traditions are main influencing factors on teachers' professional noticing.