The aim of this study was to investigate the potential of dietary 3% oyster mushroom (Pleurotus ostreatus) waste in enhancing the anticoccidial effects in broilers challenged with Eimeria tenella infection. The experiment involved a total of 600 Japanese quails, raised from one to thirty-five days of age, which were divided into four treatment groups. These included a negative control group that received a basal diet (BD) without any anticoccidial or antibiotic supplementation in the non-challenged birds (negative control, NC); a positive control (PC) group consisting of NC birds challenged with E. tenella; a group that received the BD with an anticoccidial drug (standard); and a group that received the BD supplemented with 3% waste from oyster mushrooms (3% Pleurotus ostreatus). The results showed that the feed intake, body weight gain, and feed efficiency were significantly lower in the PC (p < 0.05). However, the growth traits were similar in the standard and 3% Pleurotus ostreatus-treated groups. Similarly, there was no difference (p < 0.05) in the mortality rate, oocyst count in the feces, and lesion score between the standard and 3% Pleurotus ostreatus groups. Based on intestinal histology evaluation, the villi height and width were significantly higher in the standard and 3% Pleurotus ostreatus-treated groups compared to those of the PC (p < 0.01). In conclusion, it was found that 3% Pleurotus ostreatus effectively mitigated the low growth rate of Japanese quails induced by coccidial infection.