Mabroom date (Phoenix dactylifera L.), which belongs to the Arecaceae palm family, hasgained considerable importance as a staple food source for millions of people worldwide. This species is recognized as one of the most important agricultural crops in Qatar. Fresh fruit dates are susceptible to mold and postharvest bacterial spoilage, resulting in significant financial losses. Octanoic fatty acid (OFA) has been shown to regulate the growth of disease-causing organisms such as fungi and bacteria. It is known to have antibacterial properties. The objective of the current study was designed to evaluate the effect of OFA on postharvest pathogens of mabroom fruits under in vitro conditions. Fresh, healthy, and fully ripe mabroom dates were obtained from the National Agriculture and Food Corporation (NAFCO). The chosen fruits were packed in sterile, well-ventilated plastic boxes and transported under controlled conditions. Then, the fruits were distributed into five groups (G1 to G5). The groups G1, G2, and G3 received 1, 2, and 3.5% OFA, respectively, while G4 was left untreated and G5 was washed only with tap water. Each group contained 200 g of fresh and healthy semi-soft dates. The samples were then dried and incubated in a humidity chamber at 25°C ±2 for seven days. Signs and symptoms of decay were monitored and recorded. The presence of pathogens was confirmed by way of phenotypic- and microscopic-based methods. The results showed a significant difference (P ≤ 0.05) between the groups. OFA at 3.5% had the strongest inhibitory action against postharvest pathogens, followed by OFA 2%. However, there were no differences (P ≤ 0.05) between OFA 1% and the control groups. Aspergillus niger, Penicillium spp., Rhizopus spp., and Botrytis spp. were most abundant in the control group, followed by OFA 2% and OFA 1%, respectively. In conclusion, octanoic fatty acid at 3.5% may improve the quality of date fruit through its high antimicrobial activity, reduce the effect of post-harvest decay, minimize the loss of date fruit during storage, and improve the sustainability of date fruits.