Abstract: Seven genera and 14 species were collected from 20 poultry feed samples collected from Sohag City, Egypt. Aspergillus flavus was the most dominant species representing 53% of the gross total count of fungi. Twenty randomly-selected isolates of A. flavus, one from each sample, in addition to a reference strain (IMI 102135) were grown on 5 sodium chloride concentrations at 25 ±2°C to test their effect on some growth parameters of the isolates including macroscopic and microscopic features, in addition to aflatoxins production. The toxicity of cleaned crude extracts of the twenty fungal isolates and the reference strain against the green alga Chlorella vulgaris Bejerinck was assessed. Five isolates, in addition to the reference strain, were highly toxic, three moderately toxic and the rest were low. TLC revealed that in two high toxic isolates and the reference strain, aflatoxins B1, B2, G1, and G2 were detected, whereas aflatoxins B1 and G1 only were detected in the cleaned crude extract of nine other moderately and low toxic isolates. None of the isolates that had no biological toxicity on Chlorella vulgaris produced aflatoixns. High concentration of sodium chloride (10%) inhibited completely the growth and accordingly aflatoxins production of all fungal strains tested. Nonetheless; while the fungal growth was significantly enhanced on 2.5 and 5% concentrations, the production of aflatoxins was only inhibited on 5% of salt. The conidial heads of the reference strain of A. flavus turned to be occasionally columnar on 2.5% salt to mostly columnar uniseriate on 5% salt rather than being typically radiate, uni- and biseriate on 0% salt. The conidiophores were markedly increased in length on 5% salt (2 mm) by merely one fold, whereas the conidial heads were moderately increased in length three times (1.1 mm) more than those grown on 0% salt (346 µm). No considerable changes were noticed on the vesicle nor the conidial shape (globose to subglobose) or diameter (3.75 µm) on the different salt concentrations used. Key words: Aspergillus flavus , aflatoxins, fungal growth, sodium chloride, feedstuff, Chlorella vulgaris