Yardlong bean (Vigna unguiculata ssp. sesquipedalis), a type of cowpea, is an important vegetable legume of Asia. Cercospora leaf spot (CLS) caused by Cercospora canescens and Psuedocercospora cruenta is an important phytopathological problem of the yardlong bean grown in tropical regions. The objectives of this study were to (i) determine mode of inheritance of resistance to CLS caused by C. canescens and P. cruenta, (ii) estimate the heritability of the resistance, (iii) estimate genetic effects on the resistance using six basic populations generated from the cross between the susceptible yardlong bean ‘CSR12906’ and the resistant grain cowpea (V.unguiculata spp. unguiculata) ‘IT90K-59-120’. Segregation for the resistance to both fungi in the F2 population fitted both 3 : 1 ratio and 13 : 3 ratio of susceptible:resistant, while that in the BC2 ((CSR12906×IT90K-59-120)×IT90K- 59-120) population fitted a 1 : 1 ratio, suggesting one recessive gene or two genes with inhibitory gene action control the resistance. Generation mean analysis showed that a simple additive–dominance model was adequate to explain the genetic control of CLS disease resistance, indicating that a single gene controls the resistance. The average number of major genes (effective factors) controlling the resistance was estimated to be 1.05 and 0.92 for C. canescens and P. cruenta, respectively. The broad-sense heritability calculated for resistance to both diseases was higher than 0.90. Altogether, these results indicated that the resistance to CLS disease caused by C. canescens and P. cruenta in grain cowpea IT90K-59-120 is a highly heritable trait governed by a single major recessive gene.