<p>Drawing on the Second Demographic Transition theory, this study investigates Taiwan's persistent son preference amidst significant advancements in gender equality and economic development. Utilizing Age–period–cohort-interaction analysis and accounting for regional disparities, the study identifies a U-shaped pattern in son preference attitudes across age groups, with a decline during reproductive years that reverses in later life. A significant period effect is observed, with an increase in son preference attitudes across regions in 2006, followed by a sharper decline in metropolitan areas beginning in 2011, while other regions experienced declines in subsequent years. This pattern suggests uneven impacts of period effects on son preference attitudes. However, the absence of significant cohort effects challenges the notion of increased liberalism among Millennial cohorts. Intra-cohort dynamics further complicate the analysis, revealing divergent trends within certain cohorts. These findings underscore the need for further investigation into the intricate dynamics of son preference attitudes in response to societal changes, emphasizing that traditional cultural norms persistently influence fertility preferences despite significant advancements in gender equality and economic development.</p>