This study aimed to determine the importance of adding organic acids in mulard ducks feeding programs. Hence, the quality of anaerobically fermented high-moisture feed, in addition to, performance, carcass traits, intestinal histology and the most common gastrointestinal pathogens were evaluated in response to different levels of organic acids (OAs). Mulard ducklings (n = 400) were randomly allocated into four groups (10 replicates each), and four fermented diets were provided randomly as follows: control fermented diet (without OAs) or fermented diets supplemented with 0.5, 1 or 2% OAs blend during the starter and finisher periods. Also, different fermentation periods were tested (7, 14, 21 and 28 days). The results showed that, OAs addition to fermented diets decreased fermentation-related nutrient loss and significantly decreased population counts of studied micro-organisms. Moreover, the concentrations of lactic and propionic acids were significantly increased, and butyric acid was decreased with increasing OAs levels. The highest body weight gain was observed in the 2% OAs group. Feed utilization was improved in the groups fed on 1% and 2% OAs, when compared to the control group. In addition, OAs supplementation to the fermented diets showed a significant positive outcome on carcass weight, breast and thigh yield. Crude protein content was also increased in breast and thigh, while, fat was decreased in breast meat. Increasing OAs level showed an inhibitory effect on cecal pathogenic microbes (E. coli, Salmonella, Campylobacter and Clostridium perfringens), and increased the beneficial bacteria population (Lactobacilli and Bifidobacterium). Intestinal length and intestinal villi height seen by light and electron microscopy (both account for the area for absorption) were increased by OAs in a dose dependent manner, leading to improved nutrient digestibility (also, the best results in this study were obtained in the 2% OAs group). Accordingly, our results demonstrated that addition of OAs to high-moisture fermented feed led to improving its quality, also, it improved intestinal histology (on the villus and cellular levels) and decreased enteric pathogenic microbes and increased beneficial bacteria, all of which were positively reflected in duckling's performance and meat quality.