The objective of this study was to evaluate the viability of real-time polymerase chain reaction (PCR) to detect Gluconacetobacter diazotrophicus in sugarcane inoculated and non-inoculated with diazotrophs which are grown under field conditions. The primer pair PAL5F and PAL5R yielded a specific band of 189 bp using real time PCR with SYBER Green I. This primer pair was the most sensitive one to detect endophytic bacteria in sugarcane plants grown under field conditions and inoculated or not with bacterium. The lower limit of detection was 5 fg of template DNA, which corresponds to 12 bacterial cells. In contrast, a cultivation-dependent approach was not capable of detecting the bacteria in the same sample. The quantification of G. diazotrophicus from field grown plants using real-time PCR and a set of specific primers can be used to determine the number of bacterial cells that colonize endophytically the plant after inoculation. A highly sensitive and specific assay was developed to quantify G. diazotrophicus in sugarcane plants grown under field conditions. This assay can be used to evaluate the occurrence of the bacterium in different sample types.