This study aims to quantitatively evaluate the biogas potential of the green alga Ulva intestinalis from the Gulf of Riga, using BMP test with sewage sludge as inoculum. Meantime the nutrients role in biomass growth has been explored. For the growing rate evaluation washed fragments of U. intestinalis were placed inside 250 ml flasks, flushed with sea water with different concentrations of NPK complex nutrient: i)0 g/mL, ii)2 g/mL, iii)10 g/mL, iv)30 g/mL, with 16/8 h day/night cycle applied. The BMP tests were oriented towards the evaluation of the impact of mechanical pre-treatment, as well as different algae/inoculum ratio (A/I) on methane yield. Unless the condition on no-treatments the effect of the following methods was tested: chopping and pestling with a pestle. The results from growing rate evaluation show that the growth of macroalgae was observed up to a certain point (typically 6-8 days of exposure) even within samples without any additional nutrients; on the contrary higher concentration has shown no growth effects. This could be explained with too high nutrient concentrations jeopardizing other conditions that are vital for macroalgae growth. The cumulative CH4 yields show an important spectrum of cumulative methane yields, with the highest one observed in 1:3 A/I in which the macroalgae were chopped (92.1±33.5 mL CH4/g VS on average), while the lowest one was observed in 1:5 A/I where the macroalgae had no pre-treatment (36.0±10.5 mL CH4/g VS). The results do not show a clear impact of the pre-treatments. The scenarios with no pre-treatment exhibited the effectiveness in a range of 9.7% - 24.6%, while the chopped ones – 14.56% - 24.8%, pre-treated with pestle – 12.9% - 24.13%. The results of this study confirm the suitability of U. intestinalis for biogas production, especially in the Baltic region.