Exposure to nitrogen dioxide (NO2), a byproduct of combustion, is associated with poor asthma control in children. We sought to determine whether gas-fueled kitchen appliance use is associated with 24-h indoor NO2 concentrations and whether these concentrations are associated with asthma morbidity in children. Children aged 5–12 years old with asthma were eligible. Mean 24-h NO2 concentration was measured in the kitchen over a four-day sampling period and gas stove use was captured in time activity diaries. The relationship between stove and oven use and daily NO2 concentration was analyzed. Longitudinal analysis assessed the effect of daily NO2 exposure on symptoms, inhaler use, and lung function. Multivariate models were adjusted for age, sex, season, and maternal education. Thirty children contributed 126 participant days of sampling. Mean indoor 24-h NO2 concentration was 58(48) ppb with a median (range) of 45(12–276) ppb. All homes had gas stoves and furnaces. Each hour of kitchen appliance use was associated with an 18 ppb increase in 24-h NO2 concentration. In longitudinal multivariate analysis, each ten-fold increase in previous-day NO2 was associated with increased nighttime inhaler use (OR = 4.9, p = 0.04). There were no associations between NO2 and lung function or asthma symptoms. Higher previous-day 24-h concentration of NO2 is associated with increased nighttime inhaler use in children with asthma.