The abundance of empty fruit bunches (EFB) is a result of many palm oil industries increasing their crude palm oil production. Composting is a good, environmentally friendly alternative to overcome EFB. Two different ratios of EFB with biosludge of pulp and paper of 1 : 1 and 3 : 2, respectively, were used in this composting. The particle size of EFB was set into three different sizes of 0.5; 1.5 and 2.5 cm. The best treatment that was obtained from this study was SR4 where the EFB particle size was 1.5 cm, and the ratio between EFB and biosludge of pulp and paper was 3 : 2, respectively. The nitrogen value of SR4 increased from 1.41% to 2.71%, and C/N ratio decreased from 36.74 to 12.17 in 90 days. The population peak of bacteria of SR4 in the thermopilic phase achieved about 33.67 x 1010 cfu/g. These two treatment combinations had shown an increase in EFB composting efficiency.