The temporality of household income level with overweight/obesity in children has not been extensively studied. Little research has been conducted to determine the impact of household income on the risk of childhood overweight/obesity over time. This population-based cohort study aimed to investigate the impact of household income on the risk of overweight/obesity over time among preschool-aged children in Taiwan. From 2009 to 2018, we recruited 1,482 preschool-aged children ( ≦ 7 y of age) from low-income households and selected age- and sex-matched controls from non-low-income households for comparison; All participants were selected from those who consistently participated in the Taipei Child Development Screening Program and were monitored for overweight/obesity using body mass index (BMI) until December 31, 2018. Low-income households were defined as those with an average monthly disposable income < 60% of the minimum standard of living expense in Taiwan. The primary outcome was childhood overweight or obesity in study participants, defined as BMI (kg/m ) ≥ 85th percentile or ≥ 95th percentile, respectively. The generalized estimating equations (GEE) model was used to determine the impact of low-income households on the risk of overweight/obesity in study participants. Over 21,450 person-years of follow-up, 1,782 participants developed overweight /obesity, including 452 (30.5%) and 1,330 (22.4%) children from low- and non-low-income households, respectively. The GEE model showed that the first group had a significantly higher risk of becoming overweight/obese than the other during the follow-up period (adjusted odds ratio aOR = 1.44, 95% CI: 1.29-1.60). Moreover, children of foreign mothers had a higher risk of becoming overweight/obese than those of Taiwanese mothers during the follow-up period (aOR = 1.51, 95% CI: 1.24-1.8). The subgroup analysis revealed a significant association between low-income households and an increased risk of overweight/obesity in children aged 2-7 years (P =.01). However, this association was not observed in children aged 0-1 years (P >.999). During the follow-up period, there was a notable correlation between low-income households and an increased risk of preschool-aged children developing overweight or obesity. Implementing health promotion initiatives aimed at reducing overweight and obesity in this demographic is crucial.