The interplay between child characteristics and parenting is increasingly implicated as crucial to child health outcomes. Based on data from a national birth cohort, this study assessed the joint effects of children's temperamental characteristics and maternal sensitivity on the development of childhood obesity. Infant temperament, assessed by maternal report, was categorized into three types: easy, average, and difficult. Maternal sensitivity, assessed by observing maternal behaviors during mother-child semi-structured interaction, was categorized into two groups: sensitive and insensitive. Child's weight and height were measured longitudinally from age two years to Grade 6 and body mass index (BMI) was calculated. Obese (≥ the 95th percentile) and overweight-or-obese (≥ the 85th percentile) were defined based on sex and age specific BMI percentiles. Generalized estimating equations were used to analyze data. The proportions of children who were obese and overweight-or-obese increased as they got older, 5.47% and 15.58% at 2 years of age, to 18.78% and 34.34% at Grade 6. Children with easy temperament and under the care of a sensitive mother were at the lowest risks of obesity and overweight-or-obesity over childhood. The joint effects of children's temperament and maternal sensitivity on overweight-or-obesity largely depended on childhood phases. For instance, children with difficult temperament and under the care of an insensitive mother had much higher risks during school age but not during early childhood. In conclusion, parents may need to tailor their parenting strategies to particular child temperamental characteristics in order to prevent and control the development of childhood obesity.