Abstract Two studies in weanling pigs were conducted to evaluate the effects of a Lactobacillus postbiotic product (LFP; Lumensa, Verdesian Life Sciences, Salt Lake City, UT) in medicated and non-medicated nursery pig diets on performance, daily fecal scores and some fecal microbiome measures. A 2 X 3 factorial factorial design with main effects of in-feed medication (0 vs 55 ppm of Carbadox) and LFP inclusion rate (0, 0.075, or 0.15%) was used in each study. In study 1, LFP in liquid form was added to the treatment diets, and in study 2 LFP in dry form was used in the treatment diets. Each study used 36 pens containing 10 weanling pigs (PIC 800 x 1050; 21 d of age) per pen, and there were 6 pens for each treatment group. A pelleted three-phase commercial nursery feeding program was used. Dry LFP product increased final body weight (BW) linearly (P < 0.05) and tended to improve gain to feed ratio (G:F; P = 0.07) in study 2. Final BW was increased (P = 0.006) in nursery pigs fed medicated diets in study 2 but not in study 1. Feeding the dry LFP in study 2 improved growth performance (P < 0.05) in nursery pigs when they were fed non-medicated diets. In study 1, it was found that feeding LFP tended (P = 0.10) to decrease final BW variability (pen BW CV) on d 42. Daily fecal scores were recorded during both studies, and no treatment effects were observed. During study 2, fresh fecal samples were collected from each pen on d 21 and d 42 for microbial analysis. The Shannon Index was found to be moderately correlated (P < 0.05) to BW results on d 21 and 42 (Study 1, r = -0.31 and 0.19; Study 2, r= -0.49 and 0.27, d 21 and d 42, respectively). It was found that feeding LFP decreased the proportion of Gammaproteobacteria, which includes several Gram-negative pathogens, on d 21 (P < 0.05). In conclusion, feeding LFP to nursery pigs as dry product may increase average daily gain in pigs fed non-medicated diets and decrease BW variability (pen BW CV) when pigs are fed nursery diets containing carbadox. Also, feeding LFP may lead to changes in the fecal microbiome.