Bioconversion of oil palm lignocellulosic biomass in the form of empty fruit bunches (EFB) as the major substrate into cellulase enzyme was studied in the laboratory. A fungal strain, Trichoderma harzianum T2008 was used to evaluate the solid state bioconversion of EFB for cellulase production. The study was conducted in two systems: an Erlenmeyer flask (EF, 500 mL) and a horizontal rotary drum bioreactor (RDB, 50 L), designed and fabricated locally. The highest cellulase activity on the fourth day of fermentation in the EF was 8.2 filter paper activity (FPA)/gram dry solids (gds) of EFB, while its activity from the RDB was 10.1 FPA/gds on the second day of fermentation. Glucosamine, reducing sugar and pH were also determined to evaluate the substrate uptake and growth conditions during the entire fermentation period.