The aim of this study was to determine the efficacy of full-fat Hermetia illucens larvae meal (HM) as a protein source in diets for the youngest turkey poults, based on growth performance and parameters of intestinal function, i.e. immune status and fermentation processes in the gut. The experiment was carried on 432 one-day-old male Hybrid Converter turkeys. The birds were randomly divided into four dietary treatment groups, with twelve replicates of nine birds each. During a four-week feeding period, the HM content of turkey diets was 50, 100 and 150 g/kg in groups HM50, HM100 and HM150, respectively. The highest HM content in the experimental diet HM150, limited by high crude fat content, replaced 1/3 of soybean meal (SBM) (295 vs. 429 g/kg) in the control diet HM0. The inclusion of dietary HM resulted in a linear increase in the dry matter (DM) content and viscosity of small intestinal contents. The highest inclusion rate of HM did not affect IgA levels, but it increased IgY levels in the small intestinal tissue compared with the control treatment. At the same time, dietary HM exerted anti-inflammatory effect by decreasing TNFα and increasing IL-6 levels in small intestinal tissue (linear and quadratic response, respectively). The dietary inclusion of HM increased the activity of selected microbial enzymes (α-galactosidase, β-glucosidase and β-glucuronidase) and butyric acid concentration in the cecal digesta. Increasing inclusion levels of HM did not affect the final body weight (BW) or body weight gain (BWG) of birds, but induced a linear decrease in the feed conversion ratio (FCR). The results of this study indicate that HM can be included in diets for young turkeys at up to 150 g/kg without compromising the immune status or growth performance of birds, intestinal development and function.