An improved liquid chromatography (LC) tandem mass spectrometry (MS/MS) method has been developed for the determination of phenolic compounds (phenyl alcohols, phenyl acids, secoiridoid derivatives, lignans and flavonoids) in virgin olive oil. The used LC technique was ultra-performance LC with columns packed with 1.7 microm particles. The obtained results (retention times, linearity, reproducibility, detection limits (LODs) and quantification limits (LOQs) for the analysis of 14 phenolic compounds in standard solutions were compared with those obtained by high-performance LC (HPLC)-fluorescence and UPLC-diode array detection (DAD). When the 1.7 microm column was used, the retention times were decreased three times with respect to conventional HPLC (5 microm). The reproducibility of these methods, expressed as relative standard deviation (RSD) in terms of concentration ranged from 0.4-5.0%. In general, the LODs and LOQs were lower in UPLC-MS/MS than the other two methodologies for all the analytes, with the exception of vanillic acid and pinoresinol which values of LODs and LOQs by HPLC-fluorescence were similar to the values obtained by UPLC-MS/MS. Afterwards, the improved UPLC-MS/MS methodology was used to determine the studied compounds in spiked refined olive oil (ROO) by combining a liquid-liquid extraction (LLE) as a sample pre-treatment technique. The recoveries of the analytes were higher than 70%, with the exception of pinoresinol and 3,4-DHPEA-EDA, which were 61% and 67%, respectively. The LODs and the LOQs ranged from 0.44-127.78 microg/kg, and from 1.11-427.78 microg/kg, respectively for all the analytes. The reproducibility of the method was lower than 3.2%. The LLE-UPLC-MS/MS was successfully applied to analyze phenolic compounds in a virgin olive oil sample within 18 min.