Investigation of novel plant-based agents might provide alternative antibiotics and thus fight antibiotic resistance. Here, we measured the ability of fruit and leaf extracts of Sorbus aucuparia (Sauc) and endemic Sorbus caucasica var. yaltirikii (Scau) to inhibit nonreplicative (Klenow Fragment-KF and Bacillus Large Fragment-BLF) and replicative (DnaE and PolC) bacterial DNA polymerases along with their antimicrobial, DPPH free radical scavenging activity (RSA), and chemical contents by total phenolic content and HPLC-DAD analysis. We found that leaf extracts had nearly 10-fold higher RSA and 5-fold greater TPC than the corresponding fruit extracts. All extracts had large amounts of chlorogenic acid (CGA) and rutin, while fruit extracts had large amounts of quercetin. Hydrolysis of fruit extracts revealed mainly caffeic acid from CGA (caffeoylquinic acid) and quercetin from rutin (quercetin-3-O-rutinoside), as well as CGA and derivatives of CGA and p-coumaric acid. Plant extracts of Sorbus species showed antimicrobial activity against Gram-negative microorganisms. Scau leaf extracts exhibited strong inhibition of KF activity. Sauc and Scau leaf extracts also strongly inhibited two replicative DNA polymerases. Thus, these species can be considered a potential source of novel antimicrobial agents specific for Gram-negative bacteria.