ABSTRACT Biochar application is an effective method for agriculture production. In order to study the biochar effect on soybean (Glycine max [L.] Merr.) seedling root growth, this study was conducted in a sand culture experiment using two soybean cultivars with different P efficiencies. Soybean was pot-grown at four biochar rates (0%, 0.15%, 0.75% and 1.5%, w/v). The results showed no difference in Cultivar × Biochar interaction on root morphologic characteristics. At 7 d after germination (DAG), biochar slightly enhanced root growth; at 10 DAG, biochar significantly increased total root length (TRL) and total root surface area (TRSA) highest by 48.4% and 27.4% (P < 0.05) at 1.5% biochar rate, respectively, compared to the control. The positive effects on root morphology by biochar were especially concentrated on fine roots (< 0.5 mm). In addition, root vitality and leaf soluble sugar content were significantly increased by both 0.75% and 1.5% biochar; shoot biomass increased maximally by 65.6% at 1.5% biochar rate compared to the control; inversely, root/shoot ratio significantly reduced by 32.3% and 23.5% at 1.5% biochar rate, respectively, at 7 and 10 DAG. We suggest that biochar had positive effects on soybean seedling growth through improving root morphology and root vitality, regardless of different P efficient cultivars