Anaerobic digestion is getting attention by its ability to degrade organic materials and produce energy at the same time.Even though most full-scale anaerobic digesters are operated as continuously fed reactors, laboratory-scale tests for designparameters would be conducted using batch or semi-batch reactors. The objective of this study was to investigate theeffect of different feeding patterns with an identical organic loading rate on the performance of laboratory-scale batchanaerobic digestion reactors. Laminaria japonica was applied as a substrate with 1.5g-VS/L.day of loading rate. Threedifferent types of feeding periods, i.e, 12, 24, and 48 hours, were applied. The reactors were operated at HRT 26.7 days,35±1oC mesophilic anaerobic condition. The methane production rates were 165.10±16.92, 120.74±40.25, and57.81±20.06mLCH4/gVS for feeding periods of 12, 24, and 48hours, respectively. Reactors fed more frequentlyproduced more methane gas and the coefficient of variation was lower. As substrate feeding period increased,concentrations of total volatile fatty acids (VFAs) increased and pH decreased. Finally, the reactor with 48 hours of feedingperiod was failed after 22 days of operation. Consequently, it was shown that feeding pattern may significantly affectperformances of laboratory-scale batch anaerobic digestion reactors and the results from laboratory tests may mislead thedesign of full-scale digesters.