Brassinazole is a synthetic triazole-type inhibitor of the biosynthesis of plant hormones brassinosteroids (BR) that play critical roles in regulating broad aspects of plant growth and development. The structure of brassinazole is similar to pacrobutrazol, a gibberellin biosynthesis inhibitor. Brassinazole has displayed the ability to induce morphological changes in dark-grown Arabidopsis. Additional experiments show that Brassinazole inhibition of plant growth can be prevented by co-application of BR. Brassinazole is a specific inhibitor of C-22 hydroxylase (CYP90B1) in BR biosynthesis, and the application use of brassinazole has emerged as an effective way of complementing BR-deficient mutants to elucidate the functions of BRs.