Background: This study was conducted to investigate the effects of each phytogenic feed additive (PFA; PFA1, bitter citrus extract; PFA2, a microencapsulated blend of thymol and carvacrol; PFA3, a mixture of bitter citrus extract, thymol, and carvacrol; PFA4, a premixture of grape seed, grape marc extract, green tea, and hops; PFA5, fenugreek seed powder) on the growth performance, nutrient digestibility, intestinal morphology, and immune response in weaned pigs infected withEscherichia coli(E. coli).Results: A total of 63 4-week-old weaned pigs were placed in individual metabolic cages and assigned to seven treatment groups. The seven treatments were as follows: 1) NC; basal diet withoutE. colichallenge, 2) PC; basal diet withE. colichallenge, 3) T1; PC + 0.04% PFA1, 4) T2; PC + 0.01% PFA2, 5) T3; PC + 0.10% PFA3, 6) T4; PC + 0.04% PFA4, 7) T5; PC + 0.10% PFA5. The experiments lasted in 21 d, including 7 d before and 14 d after the firstE. colichallenge. In theE. colichallenge treatments, all pigs were orally inoculated by dividing a total of 10 mL ofE. coliF18 for 3 consecutive days. The PFA-added groups significantly increased (P < 0.05) average daily gain and feed efficiency and decreased (P < 0.05) the fecal score at d 0 to 14 post-inoculation (PI). Tumor necrosis factor α was significantly lower (P < 0.05) in the PFA-added groups except for T1 in d 14 PI compared to the PC treatment. The T3 had a higher (P < 0.05) immunoglobulin G and immunoglobulin A concentration compared to the PC treatment at d 7 PI. Also, T3 showed significantly higher (P < 0.05) villus height:crypt depth and claudin 1 expression in ileal mucosa, and significantly down-regulated (P < 0.05) the expression of calprotectin compared to the PC treatment.Conclusions: Supplementation of PFA in weaned pigs challenged withE. colialleviated the negative effects ofE. coliand improved growth performance. Among them, the mixed additive of bitter citrus extract, thymol, and carvacrol showed the most effective results, improving immune response, intestinal morphology, and expression of tight junctions.