In this study, the effects of different doses (0.5%, 1%, 2%) of rosemary essential oil on microbiological (mesophilic aerob bacteria, psycrophylic aerob bacteria, lactic acid bacteria, Pseudomonas spp., Enterobactericeae counts) and chemical (pH, total volatile alkaline nitrogen, thiobarbituric acid) properties of whole rainbow trouts were examined. For, this purpose, decontaminats at 20 ⁰C were applied to each group containing 6 fish for 2 min and placed in polyethylene ware and covered with stretch films and stored at 4±1 ⁰C and samples were analyzed on the analysis day 0th, 3th, 6th, 9th, 12th and 15th days. Microbiological samples were prepared with a modification of USDA/FSIS chicken carcass method. According to the results of the study, decontamination with rosemary essential oils extends the shelf life of Rainbow trout. In addition, microbiological sampling method is recommended to be used in similar scientific studies because of its is easy of use coherent results