Endo‐β‐mannanase is a type of cell wall degrading enzyme that plays various roles in different developmental events and in different plants. Evolutionary analysis of the gene family may provide insight into gene function and speciation. In this study, genome‐wide analysis and expression profiling of the tomato Solanum lycopersicum and soybean Glycine max endo‐β‐mannanase gene families were performed. We identified 11 and 20 endo‐β‐mannanase genes in the tomato and soybean genomes, respectively. Sequence alignment revealed three α‐helices (αA, αB and αC) of plant endo‐β‐mannanases that were conserved in tomato, soybean and Arabidopsis. Analyses of gene structure and phylogenetic analysis suggested that loss of introns has played an important role in the evolution of endo‐β‐mannanases. Evolutionary analysis of endo‐β‐mannanases from various plant species showed that they diversified before the divergence of lower (algae and bryophytes) and higher plants. Promoter sequence analysis and expression pattern analysis revealed that endo‐β‐mannanases are not only involved in growth and developmental processes of tomato, but also associated with the stress response in plants.Abbreviations – GH, glycoside hydrolase families; CBM, carbohydrate‐binding module; ABRE, ABA responsive elements; ARFAT, auxin responsive factor; ARR1AT, cytokinin responsive element; CPBCSPOR, cytokinin enhanced element; ERE, ethylene responsive element; GARE, GA responsive element; DRE, dehydration‐responsive element; LTRE, low‐temperature responsive element; MYB/MYC, transcription factor elements under stress conditions; W‐BOX, stress responsive element.