Red clover (Trifolium pratense L.) is one of the most important legume forage species in temperate livestock agriculture. Tetraploid red clover cultivars are generally producing less seed than diploid cultivars. Improving the seed setting potential of tetraploid cultivars is necessary to utilize the high forage quality and environmentally sustainable nitrogen fixation ability of red clover. In the current study, our aim was to identify candidate genes involved in seed setting. Two genotypes, 'Tripo' with weak seed setting and 'Lasang' with strong seed setting were selected for transcriptome analysis. De novo and reference based analyses of transcriptome assemblies were conducted to study the global transcriptome changes from early to late developmental stages of flower development of the two contrasting red clover genotypes. Transcript profiles, gene ontology enrichment and KEGG pathway analysis indicate that genes related to flower development, pollen pistil interactions, photosynthesis and embryo development are differentially expressed between these two genotypes. A significant number of genes related to pollination were overrepresented in 'Lasang', which might be a reason for its good seed setting ability. The candidate genes detected in this study might be used to develop molecular tools for breeding tetraploid red clover varieties with improved seed yield potentials.