The aim of this research was to investigate the effects of the oral administration of Gum Arabic on haematological and some oxidative stress markers in Mugil cephalus. For this purpose 60 mullet caught in Faro Lake (Italy), were acclimatized and fed with commercial diet for 20 days prior to the start of experiment, which lasted 15 days. After acclimatization, fish were randomly divided into two equal groups: control group was fed with commercial pellets. Haematological profile on whole blood and sera was assessed, reactive oxygen metabolites (d-ROMs), antioxidant barrier (OXY-ads) and thiol-antioxidant barrier (SHp) were immediately assessed by means of a UV spectrophotometer. Two-way repeated data analysis (ANOVA) showed significant changes only on Thrombocyte Count (TC). In the experimental group an increase in OXY-ads and SHp levels and a significant decrease of d-ROMs were observed after administration of GA.