Background: Post-stroke spasticity frequently emerges during the early subacute phase and may interfere with motor recovery. Local muscle vibration (LMV) has shown potential to reduce spasticity in chronic stroke populations, but its effects when applied during the early phase of recovery, when neuroplasticity is heightened, remain unclear. This study aimed to investigate whether a 6-week LMV intervention initiated during the early subacute phase post-stroke can modulate the development of upper-limb spasticity and improve sensorimotor recovery in a population at risk. Methods: In this randomized, placebo-controlled trial, stroke patients (median: 29 days post-stroke) received either LMV applied to wrist and elbow flexors (INT group) or a sham intervention (SHAM group) for 6 weeks. Spasticity was assessed across 20 upper-limb muscles using the Modified Ashworth Scale (MAS), with wrist and elbow flexors as primary targets. Motor recovery was evaluated using the Fugl-Meyer Assessment for the upper extremity (FMA-UE). Spinal and peripheral excitabilities (H-reflex and Mmax) was assessed as a secondary neurophysiological outcome. Results: 42 patients were included (21 per group). After 6 weeks, wrist flexors spasticity increased in the SHAM group but remained stable in the INT group, resulting in a significant Group*Time interaction. No significant interaction was observed at the elbow flexors or for global upper-limb spasticity, although similar trends were noted. Motor recovery improved significantly over time in both groups, with greater gains in the INT group (significant Group*Time interaction on FMA-UE scores). Changes in spasticity were moderately correlated with motor improvement. No significant between-group differences were observed for spinal excitability measures. Conclusions: LMV applied during the early subacute phase after stroke appears to mitigate the progression of wrist flexors spasticity and enhance upper-limb motor recovery. These findings suggest that early peripheral neuromodulation may influence the trajectory of post-stroke spasticity and promote more favorable functional outcomes during a critical window of neuroplasticity. Further studies with larger samples are needed to confirm these results and clarify the underlying mechanisms. Trial registration: NCT05315726