A new species of isosporan (Apicomplexa: Eimeriidae) is reported from the greenfinch, Carduelis chloris (Passeriformes: Fringillidae), in England. Oocysts of Isospora daszaki n.sp. are spherical to subspherical, 18.8 × 20.3 (16.8-22.4 × 16.8-25.2) μm, with a shape index (length/width) of 1.08 (1.07-1.1). Micropyle, polar granules and oocyst residuum are absent. Sporocysts are 9.4 × 14.8 (8.4-11.2 × 12.6-18.2) μm, a shape index of 1.6, with Stieda and substieda bodies. Gamogony was seen in the ileum, and merozoites were present in blood lymphocytes.