In this study, biodegradable κ-carrageenan films containing 3% nanoclay and different amounts of rosemary extract (1, 2 and 3% v/v) were fabricated and their physical, thermal, and mechanical properties, as well as antimicrobial activity were examined. The film thickness did not change significantly by the addition of rosemary extract. UV light transmission value in the control film was 20.46%, while the value for the film with 3% v/v rosmary extract reduced to 0.13%. Elongation at break (EB%) and tensile strength (TS) of the carrageenan film without the extract were 19.07% and 15.96MPa, respectively, while after adding 3% v/v of rosemary extract, the EB and TS were increased to 27.17% and 30.77MPa, respectively. Incorporation of rosemary extract greatly reduced water vapor permeability (WVP) (5.27×10-10g/m·s·Pa in control film vs 2.14×10-10g/m·s·Pa in the film containing 3% v/v rosemary extract). More importantly, the carrageenan film with 3% extract displayed >99% inhibition against B. cereus, E. coli, P. aeruginosa, and S. aureus compared with the control film. The present study showed that rosemary extract is an excellent additive to enhance the mechanical strength and antibacterial activity of carrageenan films and can be used for active packing in food packing industry.