The present invention describes the C5,C6 Substituted and/or fused oxindole compounds useful as anti-cancer agents and process for preparation thereof. Particularly the present invention relates to C5,C6 Substituted and/or fused oxindole compounds of formula I. wherein, A=C, CH, CH2, None B=C or CH part of open chain and/or cyclic alkyl/aryl/heteroaryl moiety G=alkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalkyl, alkoxy, aryloxy-all these optionally substituted with one or more substituents D=O, N, S, OH, SH, NH, None Z=C, CH2 Ring E=aryl/heteroaryl/cycloalkyl optionally substituted with one or more substituents Ring C=aryl/heteroaryl/cycloalkyl optionally substituted with one or more substituents L=H, alkyl, alkoxy, halogen, CN, OH, amino, NO2 K=H, alkyl, alkoxy, halogen, CN, OH, amino, NO2 X=H, alkyl, alkoxy, halogen, CN, OH, amino, NO2 Y=H, alkyl, alkoxy, halogen, CN, OH, amino, NO2 R1=H, alkyl R2=H, alkyl, halogen, CN, NO2, alkoxy, amino, OH