Olive ( Oleaeuropaea L.) is one of the most important fruit crops of the Mediterranean basin and parts of Asia Minor (e.g. Iran, Syria, Turkey and Iraq), cultivated for table consumption, oil extraction and as ornamental tree. Current olive groves are estimated at approximately 960 million olive trees, of which some 945 million (98% of the total), are found in the Mediterranean basin countries where they cover approximately 9.3 million hectare. There are different olive cultivars in Iran, but the ‘Zard’ and ‘Dakal’ are dominant cultivars in Shiraz province. The major problem in their cultivation is propagation through cutting because of low rooting capacity. The traditional methods used for olive multiplication since ancient times are the purely asexual method of propagation (using suckers or cuttings) and later on the method of grafting seedlings. None of the cultivated varieties can be propagated by seed because they revert to the juvenile stage and small-fruited wild type. Mist propagation of leafy semi-hardwood cuttings is the commonly practiced method to propagate many olive cultivars. Using cutting propagation, the nursery production of olive can be sped up and the new plants can bear fruit in four years. Most olive cuttings are difficult to root. The cuttings of some olive cultivars show a better response to the indole-3-butyric acid treatment, whereas cuttings of numerous cultivars in spite of indole-3-butyric acid treatment demonstrate low rooting ability. Paclobutrazol is a growth retardant and anti-gibberellin agent that in some cases results increase in rooting. In the current research, the effect of plant growth regulators, indole-3-butyric acid (IBA) and paclobutrazol (PBZ), on rooting parameters and cuttings growth of semi-hardwood cuttings of ‘Zard’ and ‘Dakal’ olive cultivars, was investigated. The experiment was carried out in the research greenhouse of the Horticultural Department of Isfahan University of Technology. The studied treatments were four concentrations of PBZ (0, 1000, 2000, and 4000 mg.L -1 ) in combination with the IBA (2000 mg.L -1 ) treatment. The layout was as factorial experiment in a completely randomized design with four replicates per treatment and twenty cuttings per replication. Results showed that the ‘Dakal’ cultivar had the highest percentages of cutting viability, callused cuttings, rooted cuttings and callused+rooted cuttings, the higher mean root number per cutting, mean length of root per cutting and fresh and dry weights of roots per cutting as compared to ‘Zard’ one. The 2000 mg.L -1 PBZ with 2000 mg.L -1 IBA treatment significantly increased cutting viability, callused cuttings, rooted cuttings, callused+rooted cuttings, mean root number per cutting, mean root length per cutting, mean root fresh and dry weights per cutting, cutting branching, mean branch number per cutting, mean branch length per cutting and mean fresh and dry weights per cutting, in comparison with control (2000 mg.L -1 IBA only) and other treatments. According to the results of this study it is recommended that application of 2000 mg.L -1 PBZ with 2000 mg.L -1 IBA is of more importance for improvement of rooting of difficult-to-root olive cultivars that do not show better responses to IBA treatment alone. Key words: olive, semi-hardwood cuttings, IBA, PBZ, rooting ability