This study evaluated the effect of different iron sources, including iron polysaccharide complexes (SQM®.iron) and ferrous sulfate (FS) on growth performance, gut health, pathogenic bacteria load, colon microbiota, and fecal iron concentration in nursery pigs. A total of 320 weaned pigs were randomly assigned to four treatments arranged in a 2 × 2 factorial design, with the factors being sanitation conditions (clean vs. dirty) and iron sources (SQM® iron vs. FS, each at 100 mg iron/kg) to give 8 pens (10 piglets per pen) per treatment. Pigs were fed their respective diets in two phases over a 28-d period. Fecal scores, body weight (BW), and feed intake were recorded weekly. Iron content, gene expression of butyryl-CoA:acetate CoA-transferase and bisulfite reductase, and pathogenic bacteria quantification were determined in fresh fecal samples collected on d 0, d 14, and d 21. On d 28, one pig randomly selected from each pen was euthanized to sample colon digesta for 16S rRNA analysis and sample jejunal tissue and serum for gut integrity and permeability analysis. Overall, SQM® iron resulted in higher average daily gain (ADG) from d 0 to14 and average daily feed intake (ADFI) from d 0 to 28 (P < 0.05). SQM® iron resulted in higher fecal iron at d 21 and improved fecal scores at d 27 (P < 0.05). Dietary iron treatments did not significantly affect gastrointestinal integrity and permeability in jejunum and did not alter fecal microbiota composition on d 28. In conclusion, substituting 100 mg/kg added iron as ferrous sulfate with equal concentration of SQM® iron improved ADG in the phase 1 (d 0 to 14) and overall ADFI (d 0 to 28) in weaned pigs.