Strigolactones (SLs) are newly discovered plant hormones which regulate the normal development of different plant organs, especially root architecture.  Lateral root formation of rapeseed seedlings before winter has great effects on the plant growth and seed yield.  Here, we treated the seedlings of Zhongshuang 11 (ZS11), an elite conventional rapeseed cultivar, with different concentrations of GR24 (a synthetic analogue of strigolactones), and found that a low concentration (0.18 µmol L^–1) of GR24 could significantly increase the lateral root growth, shoot growth, and root/shoot ratio of seedlings.  RNA-Seq analysis of lateral roots at 12 h, 1 d, 4 d, and 7 d after GR24 treatment showed that 2 301, 4 626, 1 595, and 783 genes were significantly differentially expressed, respectively.  Function enrichment analysis revealed that the plant hormone transduction pathway, tryptophan metabolism, and the phenylpropanoid biosynthesis pathway were over-represented.  Moreover, transcription factors, including AP2/ERF, AUX/IAA, NAC, MYB, and WRKY, were up-regulated at 1 d after GR24 treatment.  Metabolomics profiling further demonstrated that the amounts of various metabolites, such as indole-3-acetic acid (IAA) and cis-zeatin were drastically altered.  In particular, the concentrations of endogenous IAA significantly decreased by 52.4 and 75.8% at 12 h and 1 d after GR24 treatment, respectively.  Our study indicated that low concentrations of exogenous SLs could promote the lateral root growth of rapeseed through interaction with other phytohormones, which provides useful clues for the effects of SLs on root architecture and crop productivity.