Vigorous growth of F1 hybrid of rice (Oryza sativa L.) may be partially attributed to the development and function of the root system, but only a few studies have been conducted in this aspect. This study was carried out to elucidate the root system development of heterotic F1 hybrid seedlings grown in culture solution for 30 days. Dry weight of a single nodal root (SNR) of F1 hybrid was always greater than that of parents, except 10 days after planting. Each representative root system of 20-day-old F1 hybrid and parents was quantitatively analyzed. Total root length and total number of root apices of SNR were also greater than those of parents. From the viewpoint of the entire root system, F1 hybrid surpassed parents in the total root length, root dry weight and total number of root apices, and each heterobeltiosis was 168, 123 and 139, respectively. As a result, the root system of F1 hybrid was not only heavier in the dry weight but also greater in length/dry weight ratio (specific root length) than that of parents. We interpreted this result that F1 hybrid had high efficiency in converting dry matter into root length increment, which may possibly ensure high nutrient collection capability.