Field trials and laboratory experiments were undertaken for monitoring the relative susceptibility of four potato varieties namely; Atlas, Spunta, Simone and Nicola to potato tuber moth (PTM) Phthorimaea operculella (Zeller) infestations. Ex-periments were carried out for two summer planta-tions during 2006 and 2007. Results obtained indi-cate that Nicola potato variety was the least sus-ceptible one among the four tested varieties. The least infestation (5.5 & 7.17) as average number of larvae/100 leaves, percentages of tuber infestation (5% & 18%) and number of larve/100 tubers (5 & 20) was recorded for Nicola variety in the two sea-sons, respectively. The analysis of variance yield-ed significant differences among the four tested varieties. Positive and highly significant relation-ships were recorded between plant age and the corresponding infestation (r = +0.91 for 2006 and +0.93 for 2007). Chemical analysis for tubers showed a positive relationship between lowest sap content of free phenol and the least level of PTM infestations. That will explain why Nicola variety is considered as least susceptible to PTM infestation where it had the least concentration of free phe-nols (19.507 ppm.). The other verities which demonstrated high concentrations of free phenols harboured the highest levels of infestation with PTM. Positive and highly significant correlation were detected between free phenols content and both tuber infestation & larval content (r=+0.80 and +0.96) respectively.