The present invention provides an epoxy resin composition for a fiber-reinforced composite material which is curable at low temperatures, has excellent flame retardancy and storage stability, and yields a cured product having excellent adhesiveness with a honeycomb core, a method for producing an epoxy resin composition for a fiber-reinforced composite material, a prepreg, and a honeycomb panel. The epoxy resin composition for a fiber-reinforced composite material of the present invention contains: a reaction product obtained by reacting 100 parts by mass of a phosphorus-containing epoxy resin containing a phosphorus atom in the backbone thereof, and not less than 5 parts by mass and not greater than 20 parts by mass of an amino-terminated butadiene-acrylonitrile rubber; an epoxy resin other than the phosphorus-containing epoxy resin; a curing agent; and a curing accelerator.