This research was conducted to assess the potential synergy impacts of Spirulina platensis (SPs) and chitosan nanoparticles (CHns)on the growth rates, hematological, biochemical parameters, and body chemical composition of the European seabass (Dicentrarchus labrax). Seabass with 2.34g initial weight was distributed in 8 hapas (15 fish/ m3) and fed twice a daily at a 5% feeding rate for 16 weeks. Four diets containing 45% crude protein were formulated and supplemented by SPs and CHns: T1: control, T2: 1‰ SPs, T3: 1‰ CHns, T4: 1‰ SPs and 1‰ CHns. Results showed that those fed additives of both S. platensis and chitosan nanoparticles observed significant variation and enhanced growth performance such as final body weight (FBW), weight gain (WG%), and specific growth rate (FCR), compared to the groups treated with the control. The results of hematological parameters showed a significant increase in the red blood cells (RBCs) count, hemoglobin (Hb) count, hematocrit (Hct) value, and white blood cells (WBCs) count. In the same trend, biochemical parameters, for instance, the concentration of the total protein, albumin, globulin, glucose, cholesterol, lactate, triglyceride, urea, creatinine, uric acid, and some minerals such as calcium, magnesium, chloride, and inorganic phosphorous showed a significant improvement in D. labrax fed a diet containing SPs or/and CHns as feed additives. In the same way, body analysis data recorded a significant difference in protein, lipid, and ash contents in fish fed SPs or/and CHns compared to the control group. More defined experiments are necessary to determine the maximum levels of these microalgae and nanoparticles in D. labrax diets.