Aspergillus flavus and Aspergillus parasiticus are fungi that produce toxic secondary metabolites known as aflatoxins. These toxins can contaminate various food and feed products, including grains and nuts, before or after they are harvested. This contamination is most commonly found in tropical countries. Many studies have demonstrated that clay additions can reduce animal aflatoxin toxicity. The objective of this research was to study how the usage of Pacitan's local bentonite, located in East Java, Indonesia, could potentially decrease the harmful effects of aflatoxin B1 in native chicken species. The Masking Gel Calcification method was used to create bentonite nanoparticles at the Center for Ceramics in Bandung, West Java, Indonesia. The in vivo study was conducted at a native chicken farm in Bantul, Yogyakarta, Indonesia, with 1200 unsexed Kampung Unggul Balitbangtan (KUB) chickens. Kampung Unggul Balitbangtan chickens were divided into 4 treatments and 6 replications, each containing 50 chickens. The diets in the treatments were named as T0 (the control group in which chickens were fed basal diet, without aflatoxin B1), T1 ( T0 + 200 µg/kg aflatoxin B1), T2 (T0 + 200 µg/kg aflatoxin B1 + 1 g/kg Factory Feed with standard factory absorbent), and T3 (T0 + 200 µg/kg aflatoxin B1 + 1 g/kg nano bentonite). Aspergillus flavus isolates from PAU Universitas Gadjah Mada were created using crude aflatoxin (FNC 2262). This study found a significant difference in KUB chicken performance, specifically in feed conversion ratio (FCR). Compared to T0, the findings indicated that T1 had the highest FCR value, followed by T2 and T3. It can be concluded that nanoparticle bentonite has a looser structure because of decreased packing density with the lowest FCR. Based on hematology analysis, it can suppress aflatoxin B1 toxicity in KUB chickens.