Provided are a phenolic-hydroxyl containing resin, an epoxy resin, and a curable resin composition containing either resin that have high flowability and exhibit high heat resistance and flame retardancy after curing, a cured composition formed therefrom, and a sealant. A phenolic-hydroxyl containing resin is prepared by reacting a polycondensate of a phenolic compound (a) and formaldehyde with an aralkylating agent. The phenolic-hydroxyl containing resin contains as essential components a monoaralkylated derivative (x1) of the phenolic compound (a) having one aralkyl group on an aromatic nucleus thereof and a diaralkylated derivative (x2) of the phenolic compound (a) having two aralkyl groups on an aromatic nucleus thereof. An epoxy resin is prepared by converting the phenolic-hydroxyl containing resin into a polyglycidyl ether.