The purpose of this study was to clarify the relationship between physical fitness and lifestyle habits such as eating and sleeping habits in relation to grit among third-year junior high school students. The results showed a positive correlation between grit and physical fitness in both boys and girls, a positive correlation between chronotype, Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, and frequency of breakfast intake in girls only, and a negative correlation between social jet lag and difference in breakfast intake time between weekdays and weekends in girls only. It was suggested that basic lifestyle habits such as eating and sleeping could be expected to improve grit.