The disclosure provides a solid form and a method for preparing the same. The solid form consists essentially of a biodegradable copolymer and an amide-containing compound. The biodegradable copolymer is semi-crystalline due to the dipole-dipole interaction between the biodegradable copolymer and the urea. The method for preparing the above solid form includes: dissolving a biodegradable copolymer and an amide-containing compound in water at a first temperature, obtaining a solution; cooling the solution at a second temperature to form a solid mixture; and the solid mixture is subjected to a freeze-drying process at a third temperature.