Abstract. Eri silkworm pupae (Samia ricini) are very interesting creatures since they can be developed as a sustainable high protein food source for human beings and animals, and their cocoons can be used for silk production. At present, Thai silk is very famous for its special qualities, whereas the requirement of pupae as food grows increasingly, in particular, canned pupae with seasoning favors. Like other food products, size uniformity is required. Therefore, in this paper, a rotary drum screen with internal screw flights was designed and constructed for separating Eri silkworm pupae into two groups with different sizes. The experiments were conducted to evaluate its effectiveness. The results show that the optimal angular speed of the screen was 20 rpm and the screw pitch value was 10 cm. These parameters resulted in the accuracy percentage of pupa screening of 94.3% and the working capacity of 8.6 kg/h.