Saline engrossed ground water of Haryana region of India can neither be utilized for agriculture purpose nor for household activities. The level of salinity in this region varies from 5-15ppt maybe a potential site for rearing high valued brackishwater fish species like Mugil cephalus (mullet), which is well known for its flesh quality. Therefore, 60 days feeding trial was conducted to illustrate the effect of protein levels on the growth performance, enzyme activities and haematological parameters of mullet reared in inland saline water (ISW). During the experimental period, potassium and magnesium fortified ISW was used with constant salinity of 10 ppt. Six isoenergetic (14 kJ g−1) and isolipidic (5%) diets with Sesbania bipinosa leaf meal (10%) were formulated containing 24% (T-1), 26% (T-2), 28% (T-3), 30% (T-4), 32% (T-5) and 34% (T-6) dietary protein and fed to 216 fingerlings (2.5 ± 0.5g) stocked randomly in triplicates. The significantly higher (P<0.05) weight gain %, specific growth rate (SGR), lower food conversion ratio (FCR), proteases, lipase, aspartate transaminase (AST) and alanine transaminase (ALT) were observed in T-5, T-6 and T-4 groups. Significantly higher (P<0.05) RNA/DNA ratio and whole -body protein was found in the T-5 group. Protein efficiency ratio (PER) and protein productive value (PPV) decreased with the increasing dietary protein level upto 28% and then increased at 30 and 32% dietary protein. Significantly higher (P<0.05) HSI, VSI, liver glycogen, body lipid was found in T-1 and T-2 groups while malate dehydrogenase (MDH), superoxide dismutase (SOD) and catalase in the T-1 group. Amylase and Lactate dehydrogenase (LDH) activities remain unaffected. Based on the present findings, it can be concluded that feeding of 30% dietary protein promote better growth performance and nutrient utilization in mullet reared in ISW.