Neurotoxin complex (NTC) genes are arranged in two known hemagglutinin (HA) and open reading frame X (ORFX) clusters. NTC genes have been analyzed in four serotypes A, B, E and F of Clostridium botulinum causing human botulism. Analysis of amino acid sequences of NT genes demonstrated significant differences among subtypes and four serotypes. Phylogram tree of NT genes reveals that serotypes A1 and B1 are much closer compared to serotype E1 and F1. However, non-toxic non-hemagglutinin (NTNH) gene is highly conserved among four serotypes. Analysis of phylogram tree of NTNH gene reveals that serotypes A and F are more closely related compared to serotype B and E. Additionally, sequences of HAs and ORFX genes are very divergent but these genes are specific in subtypes and serotypes of Clostridium botulinum. Information derived from sequence analyses of NTC has direct implication in development of detection tools and therapeutic countermeasures for botulism.