There is an increased demand for biogas in the society and one way to meet this is to use cultivated microalgae as fermentation substrate. In the present study, a co-digestion experiment was established where municipal food waste was fermented with harvested microalgae cultivated in lake water. The experiment was carried out as a laboratory batch experiment with fermentation bottles, where 0, 12, 25 and 37% of the food waste was replaced with harvested microalgae, respectively. The results showed that the biogas production was generally improved after addition of microalgae. During the first 25 days of fermentation, replacement of 12% food waste with microalgae gave the highest biogas production rate. However, higher proportions of microalgae (25% and 37%) slightly decreased the gas production rate compared to 12% and compared to using food waste alone.