The present study examined the effect of chitosan (Ch) and combination of chitosan and Thymus vulgaris essential oil (Ch+T) on the quality and shelf life of butterfly-shaped rainbow trout stored under refrigerated condition (5 ± 1°C) for 15 days. The treatments in the present study were Ch (chitosan: 2% w/v) and Ch+T (chitosan: 2% w/v and Thymus vulgaris essential oil: 1% w/v). The shelf life of the samples were determined using microbiological (total psychrotrophic count), chemical—pH, thiobarbituric acid (TBA), and total volatile basic nitrogen (TVB-N)—and textural analyses. Results showed that total psychrotrophic count decreased significantly (p < 0.05) using Ch+T coating during the entire period of storage. The treatment Ch+T resulted in lower pH, TBA, and TVB-N values in comparison with the other samples. Based mainly on our data, Ch+T treatment extended the product's shelf life by approximately 6 days in comparison with the uncoated control samples.