The present invention provides an epoxy resin having a low melting point, low melt viscosity, excellent solvent solubility, and excellent processability. Also, the present invention provides an epoxy resin composition and a cured product thereof having excellent fluidity, processability, flexibility, adhesion, and thermal conductivity. The epoxy resin is represented by general formula (I) below (Q: an alkylene chain having a C1-C9 linear part which may have a C1-C18 alkyl group in a side chain, or a linkage chain having an ether bond present between two continuous methylene groups in the alkylene chain; A: a phenylene unit in which 2 to 4 phenylene groups are bonded directly or through a linkage chain, or a naphthylene unit, n: 0 to 10). The epoxy resin composition contains the epoxy resin and a curing agent. The composition includes the epoxy resin.