Cinnamaldehyde occurs naturally in the bark of Cinnamon tress and other species of the genus Cinnamomum like Camphor and Cassia. Cinnamon bark contains Cinnamaldehyde about 80-90%. Cinnamaldehyde showed many bioactivities including inhibition of cancer cell growth,Antidiabetic, anti-fungal, anti-bacterial activities etc. The present work aims that invitro anti-cancer activity of Cinnamaldehyde on Breast cancerMCF-7 cell lines by using MTT cell growth inhibition assay. The highest percentage inhibition of cancer cell lineswas found to be 32.3%at a dose of 200µg/ml.