Abstract: The aim of the study was to determine antimicrobial susceptibility pattern and to examine the mechanism of increasing quinolone resistance of S. typhi isolates in Kerala, South India. Ciprofloxacin resistant isolates were characterized by mutation analysis of quinolone resistance determining region (QRDR) of gyrA, gyrB, parC and parE genes and the results showed that majority of the isolates were resistant to nalidixic acid. There was an increase in the number of isolates showing resistance to ciprofloxacin, ceftriaxone and ofloxacin. Multi drug resistant (MDR) S. enterica serovar Typhi were not isolated. Majority of ciprofloxacin resistant isolates carried mutation in quinolone resistance determining region (QRDR) of gyrA and strains with high level ciprofloxacin resistance carried double mutation in quinolone resistance determining region (QRDR) of gyrA and single mutation in quinolone resistance determining region (QRDR) of parC. In conclusion we reported that there was an increase in the number of S. typhi isolates showing resistance to flouroquinolones and ceftriaxone. We have found out that flouroquinolone resistance in S. typhi isolates was not plasmid encoded. We had also found out that mutations in quinolone resistance determining region (QRDR) region of gyrA play an important role in flouroquinolone resistance of S. typhi isolates and parC mutation facilitate increasing level of resistance.