This article presents the scientific results obtained from the application of the algae biomass Nostoc gelatinosum (Schousboe) Elenkin as a biofertilizer in the open field cultivation of the sunflower (Helianthus annuus). When applying the algal biofertilizer, there was a positive influence both on the soil and on the plants, manifested by a minor change of soil pH in the weak alkaline direction, the quantitative increase of the total nitrogen accumulated in the soil, the increase of the height of the plant stems and the increase of the obtained crop. It is recommended to apply the algal biofertilizer based on the cyanophyte algae biomass nitrogen fixing Nostoc gelatinosum (Schousboe) Elenkin to the cultivation of the sunflower under the conditions of the Republic of Moldova.