Aims: The study focused on screening, identification and characterization of mannanolytic actinomycetes isolated from soil and leaf litter samples obtained from several sites in Indonesia. Methodology and results: A total of 337 isolates of actinomycetes isolated from soil and leaf litter samples collected from various areas in Indonesia were screened for their mannanolytic activity. Mannanase activity was analysed using locus bean gum (LBG) as the substrate. The strain ID06-0379 displayed significant mannanase activity. The strain ID06- 0379 was analysed for its mannanase activity by determining the rate of enzyme production when cultured in the presence of palm kernel cake (PKC) as a substrate. The highest mannanase activity from ID06-0379 was 4.40 U/mL at 5% PKC concentration at 5 days incubation. Chemotaxonomic and phenotypic characterisation of mannanolytic actinomycete was done and the strain ID06-0379 contained meso-diaminopimelic acid, and madurose was the diagnostic sugar in whole cell sugar. The polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol, and hydroxy-phosphatidylethanolamine. The predominant menaquinone of strain ID06-0379 was MK-9(H4). The major cellular fatty acids were C16:0 (31.47%), cis9-C16:1 (15.23%) and iso-C16:0 (10.84%), and the G+C content of the DNA was 71.7 mol%. Phylogenetic analysis based on the 16S rDNA sequences revealed that strain ID06- 379 was closely related to species of Nonomuraea jabiensis A4036T with 99% nucleotide similarity. Conclusion, significance and impact study: The results from this study revealed that the mannanolytic actinomycete strain ID06-379 belongs to the genus Nonomuraea that closely related to N. jabiensis A4036T . Mannanase production using agricultural waste such as palm kernel cake may contribute to the development and utilisation of biomass bioconversion processes. Keywords: Indonesian actinomycetes, mannanase enzyme, locus bean gum, palm kernel cake, Nonomuraea sp. ID06- 0379.