Erbium-doped fiber amplifiers (EDFAs) with low-cost long-period fiber gratings (LPFGs) fabricated by high-frequency CO2 laser pulses are investigated theoretically and experimentally. Results shows that Performances of EDFAs for both single-wavelength and multi-wavelength applications can be improved via inserting a LPFG into the erbium-doped fiber (EDF) as an ASE noise filter or a gain equalizer. Optimization of an in-line EDFA with a LPFG is also provided. The NF of such an in-line EDFA is improved by ～0.5 dB and its small-signal gain is enhanced by 7 dB, compared with that without filtering. A multi-wavelength EDFA with a gain flatness of ～1.5 dB is simply achieved via inserting a LPFG into the middle of an EDF as a gain equalizer, accompanying with a gain improvement of ～1 dB and a NF reduction of ～0.1 dB compared with the EDFA having a LPFG located after the EDF.