The invention relates to coryneform microorganisms capable of assimilating lactose which carry a recombinant DNA capable of conferring the ability to assimilate lactose on coryneform microorganisms; and to a process for producing L-amino acids which comprises culturing said coryneform microorganism capable of assimilating lactose in a culture medium containing lactose to form an amino acid, and recovering said amino acid accumulated in the culture broth. Further, the invention relates to a method for preparing recombinant plasmids containing a DNA fragment essential to the expression of a gene in coryneform microorganisms.