Abstract: In this paper, 8 thiosemicarbazones and 12 transition metal complexes thereof have been synthesized and tested for bacteriostatic activity against five kinds of bacteria. The results show that hetero atom or substitution group in the o-position of the aryl ring to the carbonyl group in the aldehyde or ketone is essential to the bacteriostatic activity of the thiosemicarbazones, and different mechanisms of inhibition are followed by thiosemicarbazones and their complexes. The complexes displayed activity superior to the thiosemicarbazones.