Humans Serum Albumin (HSA) or an HSA fusion protein is expressed in plant plastids. A plastid transformation vector is made which contains an expression cassette that contains regulatory sequences, the coding region for HSA or an HSA fusion protein and a selectable marker coding sequence. The vector is used to transform a plant where the plant expresses the HSA or HSA fusion protein. HSA is isolated and purified from the plant. A preferred plant is tobacco.