Abstract : Streptomyces fulvissimus ATCC 27431 was studied for siderophore production. Biosynthesis of siderophore was found to be influenced by environmental factors. Out of various media tried, chemically defined low iron medium gave maximum siderophore production (94 % siderophore units). A number of carbon and nitrogen compounds were tested for their effect on growth of Streptomyces fulvissimus and siderophore production. Glycerol, sucrose and glucose were good carbon sources while ammonium chloride, sodium nitrate and urea were good nitrogen sources. Moreover, 0.05 - 0.3 M of Carbon, 0.05 - 0.1 M of Nitrogen sources and 20 - 30 mM of phosphate was required for maximum siderophore production (92 % siderophore units). Increase in Fe (III) concentration > 5 ?M had a negative effect on siderophore production. Optimum pH for siderophore production was 8 while temperatures below 20 ºC and above 40 ºC were not suitable for culture growth and siderophore production. To the best of our knowledge this is the first report on effects of environmental factors on siderophore production by S. fulvissimus.