BACKGROUND: Nowadays, the tendency to use food packaging with antimicrobial activity of natural origin has increased. The use of edible and biodegradable films has been considered as an appropriate alternative to non-degradable plastic coatings. OBJECTIVES: In this study, the effect of coating with wheat starch and Pennyroyal (Mentha pulegium essential oil was investigated on microbial and physicochemical characteristics of rainbow trout fillet in cold conditions. METHODS: For this purpose, different treatments under the influence of starch, starch and Pennyroyal essential oil (1%), starch and Pennyroyal essential oil (2%) were prepared and physicochemical and microbial changes were evaluated at specified intervals (0, 4, 8, 12 and 16 days). RESULTS: In the microbial test, the count of total bacterial and other bacteria by starch and starch + 1% and 2%, the essential oil was decreased in different days, also the difference between the control group and other treatments was significant (p < /em>≥0.05). The highest effect of pH reduction belonged to starch + 1% and 2% essential oil in different studied days. The level of pH was not different among different treatments on day 0 of storage. However, there was a significant difference between the control group and treatments on the fourth, eighth, twelfth, and sixteenth days of storage (p < /em>≥0.05). The results of the oxidative test showed that on the 16th day of storage, the lowest level of TBA was related to the treatment with starch + 2% essential oil and the highest value was related to the control group. In fact, the application of the coating layer delayed the oxidation process. CONCLUSIONS: This study demonstrated antioxidant and antibacterial properties of the composition of edible starch and pennyroyal essential oil on the increased shelf-life of Rainbow trout fillet.