Spasticity is motor dysfunction after Spinal cord injury (SCI). Current treatments of spasticity focusing on muscle contraction have some issues (Figure.1). Phospholipase D coupled metabotropic receptor expresses in Ia fiber endings in muscle spindle and enhances Ia fiber activity. Dihydroxyphenyl glycine (DHPG) work as the antagonist of it. We hypothesized that inhibition of Ia fiber activity using DHPG reduce spasticity. Aim of this study is to confirm effect of continuous inhibition of Ia fiber activity on spasticity symptom and Ia-α connection after SCI. SCI models were made by semi-transecting 6th cervical cord. The drug was administrated with osmotic pump during 1 week from 2-week post injury. We confirmed on spasticity by weakened of Rate Dependent Depression (RDD) of Hoffman’s reflex (H-reflex) post injury. In DHPG group, H-reflex RDD were significantly normalized comparing vehicle group. Furthermore, axonal sprouting of Ia fibers projecting α motor neuron was also significantly decrease by DHPG administration; however, Ia-α connections were significantly increased after SCI. On the other hand, α motor neuron activity which is reported as pathological feature of spasticity was still higher than sham mice after DHPG administration. Skilled motor function using with single reach task was not different between DHPG and vehicle mice at 4-week post SCI, that is, there was no inhibition of functional improvement by DHPG. In conclusion, the Ia fiber continuous inhibition improved Ia-α over connection and spasticity. However, the inhibition of Ia fiber activity is not completely treatment for motor functional improvement.