<p>Marine cyanobacterium <i>Synechococcus</i> is known to accumulate substantial silicon (Si) and may thereby facilitate deep-sea vertical transport of biogenic C and Si. This raises the question of whether its phylogenetically related counterpart, <i>Prochlorococcus</i>, exhibits a similar capacity for Si accumulation. Given the ecological importance of <i>Prochlorococcus</i> in oceanic ecosystems and its role in global biogeochemical cycles, understanding its interaction with silicic acid is of significant interest. However, the capacity of <i>Prochlorococcus</i> to accumulate Si and the physiological impacts of silicic acid remain poorly understood. We assessed how<i> Prochlorococcus</i> MED4 physiologically respond to silicic acid [Si(OH)₄] concentrations spanning 1 to 50&#xa0;μM. We found that <i>Prochlorococcus</i> contained small amounts of Si that were water-insoluble, and this cellular Si content was unaffected by variations in [Si(OH)₄]. The specific growth rate and photosynthetic performance of <i>Prochlorococcus</i> were also unaffected by varying silicic acid concentrations. Interestingly, the cell size decreased with increasing [Si(OH)₄], suggesting a subtle morphological response. However, the surface elemental composition, as well as the mechanical and electrical properties of cells remained unchanged. Furthermore, variations in [Si(OH)₄] had minimal impact on both the adsorbed and cellular metal concentrations. In general, our findings indicate that <i>Prochlorococcus</i> has a limited capacity for Si accumulation and maintains physiological stability under different silicic acid conditions. This study provides a preliminary exploration into how varying [Si(OH)₄] levels influence the physiological performance of the picocyanobacterial <i>Prochlorococcus.</i></p>