Agro-industrial activities generate millions of tons of residues all over the world. Although many of them contain bioactive compounds, they are underexplored. Ethanolic extracts of beetroot stems (EEB) and guava pomace (peels, seeds) (EEG) were analyzed to assess their chemical composition (phenolic compounds and chemical profile by GC-MS) and antioxidant activity (EC50 and ABTS). Posteriorly, EEB and EEG were added to processed chicken meat, which was cooked and stored in vacuum and aerobic packages at 4 ± 1 °C for 14 days, to assess their oxidative stability and color. EEB presented higher content of phenolic compounds and antioxidant activity compared to EEG. Using GC-MS, we identified 11 phenolic compounds in EEB and EEG. When added to chicken meat, EEG and EEB retarded lipid oxidation compared to the control after 14 days of storage in aerobic packages. In general, in both packages the natural extracts proved to be as effective as BHT to maintain oxidative stability of chicken meat.