Reference genes are essential for the normalisation of the expression data of quantitative real-time PCR for the purposes of validation. Although several reference genes have been validated for the olive, comprehensive analyses including an excessive number of candidate reference genes still require study in various olive tissue samples. In this work, a total of 40 candidate reference genes were tested for their stability in 8 different olive tissues (root, apical bud, lateral bud, pedicel, young leaf, mature leaf, fruit mesocarp, and seed) with the utilisation of the most popular software programs including GeNorm, NormFinder, BestKeeper, and Delta C-t. The analyses of expression stability of candidate reference genes using quantitative real-time PCR demonstrated ubiquitin-conjugating enzyme (UBC1) as the most stable reference gene for the studied tissues of the olive. The GeNorm software also calculated the optimum reference gene combinations as two which consist of UBC1 and the Clathrin adaptor complex medium subunit (CLATHRIN) genes. This study provides the most stable reference gene combination for normalisation of target genes for quantitative real-time PCR gene expression studies on the olive.