Abstract Frass is the leftover material from the production of black soldier fly larvae (BSFL), which includes chitin-containing exoskeleton shedding, small, processed larvae, leftover dietary substrate, and larvae excrement. A total of 120 nursery pigs (initial body weight of 6.85 ± 0.10 kg) weaned at 21 d of age were used in a 6-wk study to evaluate the effect of increasing dietary levels of frass on growth performance, diarrhea score, and serological indices. Pigs were randomly assigned within sex and body weight blocks to 1 of 3 dietary treatments using 30 pens (4 pigs/pen; 10 replicates/treatment). Diets were prepared from a common basal and fed in 3 dietary phases of 2 wk each and included: 1) a control diet based primarily on corn and soybean meal; 2) the control with 3% added frass; and 3) the control with 6% added frass. On d 4, 7, and 14, individual fecal samples were obtained using fecal loops and were evaluated on a scale of 1 to 5 representing hard, normal, soft, watery soft, and watery liquid feces, respectively. Blood samples were collected on d 42 from 1 median pig per pen for the analysis of serum chemistry. Data were analyzed using the mixed model procedures as a randomized complete block design using linear and quadratic contrast comparisons to determine the effects of frass. Supplementation of frass linearly increased average daily gain (ADG) from d 7 to 14 (P = 0.044; 347.9, 378.8, and 396.8 g/d for 0, 3, and 6% frass, respectively), and tended to linearly increase ADG during Phase 1 (P = 0.079; 265.1, 284.8, and 298.6 g/d). No differences were observed for final body weight (P ≥ 0.146; 29.90, 31.48, and 30.70 kg for 0, 3, and 6% frass, respectively), and overall ADG, average daily feed intake (ADFI), or gain to feed ratio (G:F). Diarrhea scores increased (P < 0.001) from d 4 (2.96) to d 7 (4.20) and then decreased (P < 0.001) on d 14 (3.69). Inclusion of frass at 6% had a decreased diarrhea score compared with 3% frass on d 7 (P = 0.029), but pigs fed 6% frass had a greater diarrhea score (P = 0.038) than pigs fed the control diet on d 14. However, scores were indicative of diarrhea for all treatments on d 7 and 14. Serum concentrations of total protein, albumin, globulin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, γ-glutamyltranspeptidase, urea N, creatinine, glucose, Ca, P, Mg, K, Na, Cl, triglycerides, amylase, cholesterol, and creatine phosphokinase measured on d 42 were not different (P > 0.093) between treatments. All serological analytical results were generally within normal expected ranges. In conclusion, these findings suggest that dietary inclusion of frass may improve growth performance of nursery pigs, especially during the early stages of the nursery period.