The doctrine of ‘best interests of the child’ has guided courts in determining post-divorce child custody cases in Taiwan since 1996 amendments to the Civil Code. Amended Article 1055-1 requires judges to consider factors such as ‘the age, sex, and wishes of the child’ and ‘the age, occupation, character, health condition, economic condition, and lifestyle of the parents.’ However, previous studies have not clarified which factors judges consider primary. This article collects Taiwanese family court decisions from 2012 to 2017, involving 1,126 children whose parents were both Taiwanese and who both sought to acquire custody, in which Taiwanese district courts granted sole custody to the husband or wife. The article employs decision tree methodology, a commonly used machine learning technology. The article concludes that the three most significant factors considered by Taiwanese judges are first, which parent is the child's current primary caregiver, followed by the wishes of the child and the judge's assessment of parent-child interaction. This result runs counter to widely held beliefs that parental gender and parents’ occupations and economic resources are still prime factors in judges’ contemplation. Decision tree learning, we suggest, can assist parents’ and lawyers’ case evaluations and speed up extrajudicial custody determination arrangements.