Cowpea is an important pulse crop grown in sub-Saharan Africa and in parts of Asia and the Americas. Cowpea seed is an affordable source of nutrients rich in protein with number of essential amino acids. Dehulled seeds of eight improved cowpea lines grown in N’Djamena and Bebedjia (Chad) were analyzed for seed protein content in order to assess the variability, the heritability and the effect of environment interaction. In each locality, the experimental design was a triplicated randomly complete block design. The results showed a wide variability among genotypes for crude seed protein content. The mean value of crude seed protein content was 25.55% with varieties TN-27-80, TN-985-61399 and TN-5-78 showing highest values. High heritability in broad-sense (h2 = 0.74) and moderate genetic advance (GA = 14%) estimated for this character indicated the scope for improvement through selection. The effects of genotype (83.1% of the total sum of square), location (3.5%) and their interaction (13.4%) were highly significant (P<0.01), but the protein content was slightly influenced by the environment. High potential for breeding programs is expected as genetic factors are believed to account for the main variation in protein content. This research could provide information for breeders to develop cowpea cultivars with higher protein content.