A new minor dimmeric ester from seeds of Cassia fistula L. (Leguminosae). Bioactivity-guided fractionation of n-hexane phase from MeOH extract of the seeds of Cassia fistula L. (Leguminosae) yielded two bioactive substances against Cladosporium cladosporioides and C. sphaerospermum. After spectroscopic analysis, these compounds were characterised as the known benzyl 2-hydroxy-3,6-dimethoxybenzoate and its dimer dibenzyl 2,2''-dihydroxy-3,6,3″,6″-tetramethoxy-biphenyl-1,1''-dicarboxylate, which showed a new structural arrangement.