Closed-system microwave-assisted extraction was applied to extract total phenolics from spruce (Picea abies) bark, using 96.6% ethanol as an extractant. The influence of particle size (0.3; 1.0; 2.5 mm), time (3 to 20 min), and temperature (60; 80; 100 °C) on polyphenol recovery was also studied. Higher extraction temperature and smaller particle size resulted in a higher yield of extracted polyphenols. However, the effect of extraction time on yield was more complicated. The effect of all three factors is tentatively explained.