A spherical composite particle comprising: a core particle containing at least one polymer; and a chitin nanofiber layer formed of chitin nanofibers containing an ionic functional group on a surface of the core particle, wherein the core particle and the chitin nanofibers are bonded to each other in an inseparable state in which the chitin nanofibers and the core particle are not separated from each other, and the coating state of the core particle with the chitin nanofibers is maintained even after repeating an operation in which a dispersion liquid containing the composite particles is centrifuged to remove a supernatant and then a solvent is added to redisperse the composite particles, thereby purifying and washing the composite particles, or an operation in which the composite particles are repeatedly washed with a solvent by washing with filtration using a membrane filter, an amount of the ionic functional group of the composite particle, as determined according to the description, is 0.0002 mmol/g or greater and 0.5 mmol/g or less with respect to a dry weight of the composite particle, and the core particle is a biodegradable polymer, characterized in that the chitin nanofibers are fibrous chitin that has a number average minor axis diameter of 1 nm or longer and 1000 nm or shorter, which is obtained as an average value of the minimum diameters of 100 fibers measured by observation with a transmission electron microscope or observation with an atomic force microscope, and a number average major axis diameter of 50 nm or longer, which is obtained as the average value of the maximum diameters of 100 fibers measured by observation with a transmission electron microscope or observation with an atomic force microscope; and that the number average major axis diameter is 5 or more times longer than the number average minor axis diameter. a core particle containing at least one polymer; and a chitin nanofiber layer formed of chitin nanofibers containing an ionic functional group on a surface of the core particle, wherein the core particle and the chitin nanofibers are bonded to each other in an inseparable state in which the chitin nanofibers and the core particle are not separated from each other, and the coating state of the core particle with the chitin nanofibers is maintained even after repeating an operation in which a dispersion liquid containing the composite particles is centrifuged to remove a supernatant and then a solvent is added to redisperse the composite particles, thereby purifying and washing the composite particles, or an operation in which the composite particles are repeatedly washed with a solvent by washing with filtration using a membrane filter, an amount of the ionic functional group of the composite particle, as determined according to the description, is 0.0002 mmol/g or greater and 0.5 mmol/g or less with respect to a dry weight of the composite particle, and the core particle is a biodegradable polymer, characterized in that the chitin nanofibers are fibrous chitin that has a number average minor axis diameter of 1 nm or longer and 1000 nm or shorter, which is obtained as an average value of the minimum diameters of 100 fibers measured by observation with a transmission electron microscope or observation with an atomic force microscope, and a number average major axis diameter of 50 nm or longer, which is obtained as the average value of the maximum diameters of 100 fibers measured by observation with a transmission electron microscope or observation with an atomic force microscope; and that the number average major axis diameter is 5 or more times longer than the number average minor axis diameter.