Crystalline solid forms of the anti-HCV compound (S)-isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)(phenoxy)phosphorylamino)propanoate (Compound I) are described Also provided are processes of making and methods of using the crystalline forms.本發明描述結晶固體型之抗HCV化合物(S)-異丙基2-((S)-(((2R,3R,4R,5R)-5-(2,4-二合氧基-3,4-二氫嘧啶-1(2H)-基)-4-氟-3-羥基-4-甲基四氫呋喃-2-基)甲氧基)(苯氧基)磷醯胺基)丙酸酯(化合物I)本發明亦提供該結晶型之製造過程及使用方法。