Forty nine Cowpea accessions were tested in 7 x 7 triple lattice design at Haramaya University research farm, Dire Dawa in 2010/011. The objectives of the study were to estimate the extent of genetic variability for yield and yield related agronomic traits and to estimate heritability in broad sense and expected genetic advance due to selection among the forty nine cowpea accessions analysis of variance using triple lattice design revealed that there was statistically significant difference among the forty nine accessions for all the traits studied. High phenotypic coefficient of variation (PVC) was recorded for number of pod per plant, yield per plant, seed yield (kg/ha), plant height. Similarly, high genotypic coefficient of variation (GVC) was observed for 100-seed weight, plant height, number of pods per plant, yield per plant, pod length and seed yield. High heritability coupled with high expected genetic advance was estimated for days to 50% flowering; moderate heritability values coupled with relatively higher genetic advance were observed for seed yield and plant height. This indicates that these traits could be improved through selection.