Exogenously applied lysophosphatidylethanolamine (LPE) increased the growth of primary roots and the formation of lateral roots in Arabidopsis thaliana. In the presence of brassinolide, lateral root formation induced by LPE was enhanced, implying that both LPE and brassinosteroids (BR) interact positively in the development of Arabidopsis roots. Co-treatment with LPE and BRs increased the bending activity in the rice lamina inclination assay compared to that when BRs were applied alone, suggesting that LPE seems to exert its activity via BRs activity. RT-PCR revealed that LPE did not alter the expressions of genes involved in the biosynthesis of BRs but did activate the expressions of BR signaling genes in A. thaliana. In a BR-insensitive mutant, bri1, enhanced gravitropic response by LPE in wild-type A. thaliana was diminished. In conclusion, LPE is a positive regulator for the growth and development of Arabidopsis roots, and this process seems to be enhanced by BR signaling rather than by increase in endogenous levels of BRs in A. thaliana.