Abstract: Deoxyribonucleic acid-silver nanoclusters (DNA-AgNCs) fluorescent probes were synthesized by chemical method and used for selective fluorescence detection of tryptophan synthetase β chain gene of Chlamydia trachomatis (the target sequence). Two DNA probes and argenti nitras were added into the pH 6.6 acetate buffer solution to synthesize DNA-AgNCs with high fluorescence intensity in the presence of reducing agent of sodium borohydride. The target sequence solution and DNA-AgNCs solution were added into the pH 5.5 ammounium acetate buffer solution, and the mixed solution was made its volume up to 100 μL the concentration (caculated by DNA) of DNA-AgNCs reached to 1.5 μmol·L^-1, and reacted for 10 min at 15 ℃. The target sequence was hybridized with one of the 2 DNA probes, and the structure of DNA-AgNCs was destroyed, resulting in fluorescence quenching. It was shown that DNA-AgNCs particles were spherical in shape with particle size of about 2 nm, good dispersion and no aggregation. The excitation and emission wavelengths of fluorescence were at 558, 610 nm, respectively. Linear relationship between values of the concentration of the target sequence and the ΔF (the difference between fluorescence intensities of the detection system after and before adding of the target sequence) was kept in the range of 0.23-1.10 μmol·L^-1, with detection limit (3s/k) of 57 nmol·L^-1, and RSDs (n=11) of the determined values ranged from 1.5% to 4.9%. Adding the target sequence and 10 times of the target sequence concentration of homologous sequence, symptom similarity sequence, Chlamydia sequence and random sequence, the detection system showed fluorescence quenching effect when the target sequence was added, indicating that the synthesized fluorescent probe had excellent selectivity. Test for recovery was made by standard addition method using HeLa cell lysate and fetal bovine serum as simulated matrices, giving recoveries in the range of 98.0%-100%.