The extracts of Padina pavonica (a macroalgae, ME), Rubus fruticosus (blackberry) leaves (BE), Juniperus oxycedrus waste (JWE) and Juniperus communis needles (JE) were used to evaluate their potential effects on chemical, microbial and organoleptic qualities of sea bass (Dicentrarchus labrax). The sensory assessment showed that fish fillets treated with BE, JE and ME were preferred more by the panellists, and rejected at 18 days of storage compared to the control (12 days). All extracts (except JWE) together with modified atmospheric packaging (MAP) decreased the values of biochemical parameters of sea bass fillets. TVB-N, PV, FFA, TBA values remained lower in treatment groups. Microbiological results were consistent with sensory results. Although microbial growth showed a rapid increase in the control and JWE groups during storage, BE, ME and JE groups significantly inhibited the bacterial growth in fish meat (p < 0.05). Lactic acid bacteria in sea bass fillets under MAP condition increased slightly during storage and reached the highest levels in the control and JWE groups, respectively, with the value of 5.60 and 5.52 log cfu/g at the end of storage. This study showed that all extracts except JWE together with MAP application extended the shelf life of sea bass fillets up to 18 days compared to the control (12 days), exhibiting potential antioxidant and antimicrobial agents in seafood industry.