Pummelo (Citrus maxima (Burm.) Merr.) cultivar Tabtimsiam is the new cultivar growing in Pak Panang Basin, Nakhon Si Thammarat, southern of Thailand. It is the one of the most acceptable tropical fruit of consumers. Canker caused by Xanthomonas axonopodis pv. citri is the most seriously damage especially on fruit. This research was conducted to monitor disease severity and trialed for screening fungicides, antibiotics, and antagonistic bacteria to solve this disease at farmer orchards. The severity of canker monitoring on Tabtimsiam pummelo at 3 - 5 and 6 - 8-year age plant, on leaf was high at 11.85% and 16.37% and mature fruit was 16.15% and 17.12%. The result for controlling agent screening indicated that tetracycline was the highest control of 1.12 cm inhibition zone. It higher than streptomycin and ampicillin of 1.02 and 0.95 cm inhibition zone and also distinguish higher than broad spectrum fungicide, copper hydroxide and copper oxychloride of 0.57 and 0.46 cm inhibition zone respectively. For antagonistic screening, only the one antagonistic bacterial, Bacillus amyloliguefacien KPS 46 expressed of secondary metabolite to inhibit X. a. pv. citri of 0.14 cm inhibition zone, while Bacillus subtilis and Paenibacillus pabuli SW01/4 did not express antagonism by produced secondary metabolite to inhibit this pathogen.