Succinate cytochrome c reductase (SCR) from mice liver was inhibited in vivo and in vitro by some antibacterial drugs like cefaclor, cephalexin, and antifungal drug, atpenin A5. The inhibition was observed for the enzyme towards the reduction of both 2,6 dichlorophenol indophenols (DCIP) and cytochrome c (cyt c). The inhibition of the antibiotics was a mixed type with respect to the reduction of DCIP and cyt c. In vitro, Atpenin A5, cefaclor and cephalexin inhibited the enzyme with respect to the reduction of DCIP in a mixed type manner with Ki values of 3.43 x 10-10, 1.82x 10-9 and 2.40x 10 -9 M respectively. Also, atpenin A5, cefaclor, and cephalexin inhibited the enzyme with the respect to the reduction of cyt c in a mixed type manner with ki values of 5.07x10-10, 6.60x 10-9 and 4.38 x 10-9 M respectively. The inhibition of SCR in vitro and in vivo treated by cefadroxil was not clear.