Starch was isolated from four-o'clock flower (Mirabilis jalapa L.) seed by an alkaline process and selected physicochemical properties was determined. The nearly spherical starch granules were approximately 1.5–3.0 μm in diameter. The starch had a pasting temperature of 72.5°C, and an iodine affinity of 3.6%. The Bra-bender viscoamylogram and the swelling pattern indicated the starch underwent restricted swelling. The starch contained only trace amounts of phosphate. Solubility in dimethyl sulfoxide was low, but after being treated with bacterial alpha-amylase, the solubility was high. The degree of syneresis of the pasted starch during storage was high and freeze-thaw stability was low. The properties of this isolated small-granule starch differed from other such starches reported in the literature.