The absolute frequency of~(87)Rb 5S_(1/2)(F=2)→5D_(5/2)(F″=4) two-photon transition at 778 nm is measured in an accuracy of 44 kHz.A home-made erbium-doped fiber laser frequency comb with frequency stability of5.0 ×10~(-13)@1s is employed for the light source.By using a periodically poled lithium niobate,the femtosecond pulse operating in 1556 nm is frequency-doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor.Through sweeping the carrier envelope offset frequency(f_(ceo)),the 5S_(1/2)(F=2)→5D_(5/2)(F“=4)two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve.After the frequency correction,the measured result agrees well with the previous experiment on this transition.The entire system configuration is compact and robust,providing a potential candidate of optical frequency standard for telecommunication applications. The absolute frequency of ~ (87) Rb 5S_ (1/2) (F = 2) → 5D_ (5/2) (F ”= 4) two-photon transition at 778 nm was measured in an accuracy of 44 kHz. A home-made erbium-doped fiber laser frequency comb with frequency stability of 5.0 × 10 ~ (-13) @ 1s is used for the light source. BY using a periodically poled lithium niobate, the femtosecond pulse operating in 1556 nm is frequency- doubled to 778 nm to obtain the direct two-photon transition spectroscopy of thermal rubidium vapor. Through sweeping the carrier envelope offset frequency (f_ (ce)), the 5S_ (1/2) (F = 2) → 5D_ (5/2 ) (F "= 4) two-photon transition line is clearly resolved and its absolute frequency is determined via the peak-finding of the fitting curve. After the frequency correction, the measured result agrees well with the previous experiment on this transition. The entire system configuration is compact and robust, providing a potential candidate of optical frequency standard for telecommunication applications.