Abstract: This investigation consisted of four experiments, i.e., two pot experiments were carried out under glasshouse conditions and another two experiments were conducted under field conditions. The glasshouse pot experiments were carried out at Mahasarakham University, whilst the field experiments were carried out at Khon Kaen University. Twelve cowpea cultivars were used for both the first glasshouse and the first field experiments. The second glasshouse experiment had 14 cowpea cultivars and the same number of cultivars was used for the second field experiment. The four experiments aim to search for outstanding cowpea cultivars where they manifest high resistance to Pseudocercospora leaf spot disease for further breeding programme. A Completely Randomized Design (CRD) with four replications was used for both glasshouse experiments, whilst a Randomized Complete Block Design (RCBD) with four replications was used for both field experiments. The results showed that eight out of fourteen cowpea cultivars of the glasshouse and field experiments possessed a ranking score of Immunity (I). They were ranked accordingly as the best gene resources for future breeding programme. They include IT84E-1-108 as the best cultivar followed by KKU35, Ubonrachatanee1, KKU305, KKU264B, KKU264R, KVC#7 and IT86D-812 with seed yields of the field Experiment 2 of 1,480, 944, 864, 860, 738, 714 and 614 kg ha-1, respectively. The spread out of the disease was encouraged most by high relative humidity of the environmental conditions.