Plant hormone brassinosteroid (BR) can improve the drought resistance of plant.This study explores the effects of spraying BR on the expression of transcription factor BES1/BRI1 in cotton seedling under drought stress.It is helpful for elucidating the mechanism of BR improving the drought resistance of cotton.The BES1/BZR1 gene was cloned by using PCR technique from the seedling of cotton‘XLZ17’(Gossypium hirsutum) and named as GhBES1/BZR1 (GenBank accession number KP272000).Sequence analysis indicated that GhBES1/BZR1 contains an open reading frame (ORF) of 960 bp,which encodes 319 amino acids included a conserved domain DUF822.The calculated molecular weight is 34.3 kD and the theoretical isoelectric point is 8.95.After 2.5% PEG-6000 treatment for 24 h,water,BR (brassinosteroids) and Z (BR inhibitor) were sprayed on the seedlings of cotton‘XLZ17’,respectively.The effects of spraying BR on the expression of GhBES1/BZR1 were analyzed by the real time quantitative PCR(qRT-PCR).The results showed that the expression levels of GhBES1/BZR1 were greatly increased after BR spraying within 3 h,and then the expression levels of GhBES1/BZR1 were significantly decreased after 6 and 12 h.The results demonstrated that spraying BR quickly up-regulated the expression of GhBES1/BZR1 under drought stress,which might be contributed drought resistance of cotton.