Abstract: The unicellular green alga Haematococcus pluvialis accumulates a highvaluable astaxanthin under stress conditions. Betacarotene ketolase (BKT), a key enzyme in astaxanthin biosynthesis in H. p luvialis, catalyzes the conversion of B-carotene to canthaxanthin and zeaxanthin to astaxanthin. Electrophoresis mobility shift assay (EMSA) was used in H. pluvialis to identify transcription factor binding sites within a 309 bp promoter region (-617/-309) of betacarotene ketolase gene and a 59 bp sequence between -396 and -338 bp was found to have a specific binding activity to the nuclear protein. Sequence analysis revealed that this important functional region contains neither TATA nor CAAT box but a Gbox involved in the responsiveness of light, anaerobiosis, pcoumaric acid and hormone.