A sustained-release injection, which comprises a suspension of a powder comprising an active ingredient and a pharmaceutically acceptable biodegradable carrier (e.g. proteins, polysaccharides and synthetic high molecular compounds, preferably collagen, atelocollagen, gelatin, and a mixture thereof) in a viscous solvent for injection (e.g. vegetable oils, polyethylene glycol, propylene glycol, silicone oil, and medium-chain fatty acid triglycerides). The sustained-release injection can release the active ingredient at an effective level for a long period of time when injected.