Optical control of magnetic anisotropy in ferromagnetic (FM) metals via non-thermal effects offers an intriguing route for the ultrafast magnetization control. Here, we report on strong modification of exchange-coupling induced uniaxial magnetic anisotropy (UMA) in Fe/CoO below the Néel temperature of CoO owing to the charge transfer excited by ultrafast laser pulses. This UMA modification by nonthermal effects is manifested as much smaller frequencies of the Fe spin precession in the initial 100-ps time range under the 400-nm pump with charge transfer excitation, compared to the 800-nm pump with pure thermal effects. From the time-dependent frequency shift under a moderate pump fluence of 0.5 mJ/cm2, we determined the magnitude of the UMA attenuation with a highest value of more than 1000 Oe in a duration of 100 ps. The strong UMA attenuation is attributed to the large suppression of the interface exchange coupling as a result of the diminishment of antiferromagnetic (AFM) spin order in CoO. Our results give insights into the ultrafast spin modulation in AFM CoO dominated by the electronic process, which can be utilized for efficient driving of the coherent spin motion in the proximate FM metal exchange coupled to CoO. This work was supported by the National Key Basic Research Program of China (Grant Nos. 2015CB921403 and 2015CB921401), the National Key Research and Development Program of China (Grant No. 2016YFA0300703), and the National Natural Science Foundation of China (Grant Nos. 51371052, 11474066, and 11434003).