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This study aimed at extracting and quantifying phenolic compounds from Cinnamomum zeylanicum and Zingiber officinale Roscoe, then subjecting them, in vitro, to screening based on their richness in polyphenols, flavonoids, and their antioxidant potential. The extraction of phenolic compounds was performed by maceration in absolute methanol. The quantification of polyphenols and flavonoids in two extracts was performed using colorimetric techniques: the Folin–Ciocalteu reagent and the aluminum trichloride. The evaluation of antioxidant activity was performed using three methods: FRAP, DPPH-radical scavenging, and H2O2 neutralization. Lipid peroxidation was evaluated using thiobarbituric acid reactive substances. In addition, antibacterial activity, using the agar diffusion and incorporation methods, was tested on four bacteria (Escherichia coli ATCC 2592, Pseudomonas aeruginosa ATCC 27853, Bacillus cereus ATCC 11778, and Staphylococcus aureus ATCC 33862). The results showed that the methanolic extract from Cinnamomum zeylanicum (MEC) was richer in polyphenols than the methanolic extract of Zingiber officinale Roscoe (MEG). A strong and highly significant antioxidant capacity was observed, with MEC compared to MEG in the three techniques used. The values determined by the FRAP test were EC50 = 108.56 ± 4.18 μg/ml versus 310.07 ± 6.94 μg/ml, respectively. The IC50 determined by the DPPH-radical scavenging method was 5.27 ± 0.11 μg/ml versus 22.50 ± 0.45 μg/ml. Consequently, a highly significant inhibition potential of lipid peroxidation was obtained with MEC compared to MEG, with MDA values of 57.68 ± 1.64 and 63.02 ± 2.95 μmol/g tissue, respectively. MEC has a strong antibacterial effect against gram-positive and gram-negative bacteria. Cinnamon exerts powerful biological activities compared to ginger. This ability could be the result of the high content of phenolic compounds in the bark.