Burkholderia pyrrocinia CH-67 is a biocontrol bacterium with strong antifungal activity against several plant pathogenic fungi. Transposon mutagenesis was performed to identify the genes responsible for the antifungal activity of B. pyrrocinia CH-67. Of the 2,500 mutants tested using the Fulvia fulva spore screening method, a mutant deficient in antifungal activity, M208, was selected. DNA sequence analysis of the transposon-inserted region revealed that a gene encoding an adenylate kinase-related kinase was disrupted in M208. Antifungal activity was restored in M208 when a full-length adenylate kinase gene with its promoter was introduced in trans. The deduced amino acid sequence of adenylate kinase from CH-67 was 80% identical to that of B. cenocepacia MCO-3. Adenosine diphosphate supplementation or high levels of adenosine triphosphate and adenosine monophosphate together restored antifungal activity in M208, suggesting that adenylate kinase of B. pyrrocinia CH-67 is involved in antifungal activity expression.