The purpose of this study was to investigate the impacts of Spirulina platensis algae extract (seaweed) and Saccharomyces cerevisiae yeast extract as bio-stimulants on the growth, flowering, and chemical composition of the Zinnia elegans plants during 2021 and 2022 seasons. When the seedlings reached about 10 cm in length, they were transplanted into individual pots filled with a mixture of clay and sand (1:1, v/v). Seedlings were sprayed with algae extract at 0.5 and 1% and yeast extract at 3 and 6 g/l however, control plants were sprayed with distilled water. The obtained results indicated that algae extract at 1% treatment increased all vegetative parameters including plant height, stem diameter, number of branches/plant, number of leaves/plant, root length, leaf area, shoot and root fresh and dry weights, flowering parameters including number of inflorescences/plant, inflorescence F.W. and D.W. in both seasons and inflorescence diameter in the second season only. The chemical composition was also positively affected by the same treatment and gave the highest values for photosynthetic pigments, total amino acids, crude protein, macronutrient elements (N, P and K%), total sugar content and total indoles followed by plants sprayed with yeast extract at 6 g/l for all the mentioned parameters during both seasons. It was concluded that algae extract at 1% or yeast extract at 6 g/l can be used as bio-stimulants to boost the growth of the Zinnia elegans plant