The research has a purpose to find the powder dosage of weeds powder (Cyperus rotundus L.) to control Tribolium castaneum and the influence about quality of corn seeds. This research was conducted at Maret until Mei 2016 in Proteksi Laboratory, Faculty of Agriculture, Muhammadiyah University of Yogyakarta. The research arranged in Completely Randomized Design with single factor laboratory experimental has 6 treatments with 3 repetitions. The treatments was dosage of weeds powder (Cyperus rotundus L.), consisted as dosage varian 0 gram, 4 gram, 8 gram, 12 gram, 16 gram / 100 corn seeds and 0,03 gram Phostoxin/1 kg corn seeds. The results of the research showed that application of 12 gram/100 corn seeds dosage of weeds powder (Cyperus rotundus L.) is effective to controlles of Tribolium castaneum with value of mortality 83,33% and value of efication 81,48%. Weeds powder (Cyperus rotundus L.) can decreased quality of corn seeds at period of storage until 3 months period