This study was conducted to reduce off-flavors from sea tangle (Laminaria japonica) extract since the typical odor of seaweed is an impediment to consumption of seaweed products. Fifty-six odor compounds emitted from the extract were identified using a thermal desorbor and gas chromatography-mass spectrometry. On the basis of expected odor intensity (EOI), isovaleric acid (41.2%), allyl isothiocyanate (22.6%), octanal (11.1%) and acetaldehyde (10.6%) were responsible for about 85.5% of total odor strength in the extract, suggesting that the odor of the extract might mainly be attributed to these compounds. The EOIs of odor compounds were dramatically reduced or disappeared during fermentation by Aspergillus oryzae. Total EOI of the odor compounds decreased about four-fold, compared with that of the raw extract (control) after the four days of fermentation at 30 degrees C with agitation at 120 rpm. These results indicate that microbial fermentation may be a good strategy to reduce off-flavors of seaweeds. (C) 2012 Elsevier Ltd. All rights reserved.