The aim of this study was to evaluate the effect of full-fat insect meals fed ‘on top’ to broiler chickens on their performance and the microbiota composition in the gastrointestinal tract. A total of 1850 day-old Ross 308 females were used in a set of four independent experiments. The insects Gryllodes sigillatus, Shelfordella lateralis, Gryllus assimilis, Tenebrio molitor and Hermetia illucens were applied in amounts that varied from 0.05 to 0.2%. In general, the application of insect meals to the diets of broilers did not affect their growth performance over the experimental period. However, the 0.2% additions of T. molitor and H. illucens increased feed intake at days 15–35 (P = 0.011) and the entire period of feeding (days 1–35; P = 0.018) (Experiment 3). Moreover, in Experiment 4 the supplementation of 0.2% of S. lateralis improved body weight gain (days 11–21 and 1–21), feed intake (days 1–10 and 1–21) and feed conversion ratio (days 1–21). The addition of insect meals reduced the pH value of digesta in the crop (Experiments 1 and 2) and in the caeca (Experiment 2). Supplementation with H. illucens caused the most significant effect on the microbiota populations in the crop, ileum and caeca (Experiment 3). However, at the higher levels of S. lateralis addition to the diets of broilers, the counts of selected microbiota in the crop and ileum increased (Experiment 4). These results indicate that the application of the insect full-fat meals in relatively small amounts can affect the microbiota composition in the gastrointestinal tract of broiler chickens.