Eu(DBM)(3)Phen doped poly(methyl methacrylate) core step-index polymer optical fiber (SI POF) has been fabricated and related properties of the doping material were discussed. Amplified spontaneous emission (ASE) at 613 nm of a SI POF with 40 cm length has been observed at ambient temperature by end-pumping with a YAG at 355 nm. The threshold of the absorbed pump power for the onset of ASE is about 0.01 mJ. (c) 2005 Wiley Periodicals, Inc.