Heterocycles having heteroatom N, S shows profound biological activities like antibacterial, antimicrobial, antihypertensive, anticancer etc. in addition to above said activities, a new series of synthesised compounds, 1,4-benzothiazine derivatives were found to show good antioxidant activity. To find the valuable bioactivity of above said ring transformed compounds, series of 4H-1,4-benzothiazine derivatives were synthesized through C-2 ring expansion of substituted 1,3-benzothiazoles. The antioxidant activities of all the synthesised compounds were screened by 2,2- Diphenyl-1-Picrylhydrazyl (DPPH) method having ascorbic acid as a standard. The synthesized compounds shows moderate to good antioxidant activity.