An indigenous osmotolerant rhizobacterial isolate has been obtained from Merapi volcano eruption ash, Central Java, Indonesia. The isolate also demonstrates phosphate solubilising, as well as a strong ammonification-nitrification capability. A study has been carried out to identify the isolate based on molecular characterisation using the 16S rDNA as the molecular character. In this work, PCR optimisation of the 16S rDNA was carried out, prior to the sequencing of the 16S rDNA, by varying the annealing time, using primer 27F and 1429R and DNA template of bacterial isolate otained from Merapi. PCR amplification was carried out by the following programme: pre-denaturation at 950 C for 2 minutes, primer annealing at 550 C for 0,5 minutes, and followed by 30 cycles of polimerisation at 720 C for 1 minute, denaturation at 950 C for 2 minutes, and primer annealing at 550 C for 0,5 menit. At the end of cycles, an extra polimerisation was carried out at 720 C for 5 minutes, and finally the temperature was cooled down to 80 C. The optimisation process resulted in strong band, with no visible mispriming, that can be used further for DNA sequencing. Keywords: Biofertiliser, Osmotolerant Rhizobacteria, PCR optimisation