Summer savory (Satureja hortensis L.) plant is one of most promising plants suitable for cultivation in the conditions of Egypt. A filed experiment was carried out at Department of Ornamental Horticulture, Faculty of Agriculture, Cairo University, with Department of Medicinal and aromatic Plants research National Research Center, Dokki, Giza, Egypt. during two successive seasons 2014 and 2015. The experimental design was a factorial in split plot with three replicates. The aim of the work was to study the effect of nitrogen fertilization at the rates of N0, N1, N2 and N3 (0, 40, 80 and 120 kg N/ feddan ) as equivalents 0.0, 200, 400 and 600 kg/feddan of ammonium sulfate fertilizer 20.5% N, respectively as the main plots. Plant spacing was defined as S1, S2 and S3 (45×50, 30×50 and 15×50 cm, respectively) between the plants, as sub-plots. The effect of these treatments on essential oil percentage, essential oil constituents and total flavonoid content of S. hortensis L. was recorded. The results showed that the highest level of N fertilizer to combined with the least plant spacing had a significant effect on increasing the essential oil percentages in both seasons. The major essential oil constituents were carvacrol (47.26 and42.90%) and γ-terpinene (38.30 and 39.10%) at the first and second cuts, respectively. Generally, carvacrol content was not affected by N fertilizer, but the γ-terpinene content increased slightly. The other lower percentage components arranged in descending order including ρ-cymene, terpinolene, α-terpinene, α-pinene and α-thujene contents were not significantly affected by such treatments. Total flavonoid content decreased with all N fertilizer levels at the first cut (June), the opposite trend was noticed at the second cut (August) in both seasons. Plant spacing at intermediate density was associated with the production of high contents of total flavonoids at both cuts during both seasons.