A Biosensor for detection of DNA sequence in bacterium Bacillus anthracis has been developed using Raman spectrum of single walled carbon nanotubes (SWNTs). We have utilized the fact that being hydrophobic in nature single strand of target DNA (diseased DNA) gets wrapped over MM. surface forming single stranded DNA-SWNT complex. The sensing ability of this sensor has been studied using the dependency of G peak intensity (in the Raman spectrum of SWNTs) on the covered surface of SWNTs. When a DNA having a sequence complementary to that of the target DNA is added to DNA-SWNT complex, hybridization between these sequences takes place. This results in large covered surface area of SWNT and reducing the intensity of G peak. A slight red shift in the G peak has also been observed. The intensity of G peak depends on the exposed area of SWNT to the excitation beam. On the other hand with noncomplementary DNA, no significant change in intensity of G peak is observed. Finally, results were cross-checked by gel electrophoresis. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.