Abstract:Aim To a research on the function and change in ultrastructure of M.fortuitum.Method Clinical strains cultured on the blood agar plate for six days was taked to observe its ultrathin with electron microscope and contrast with standard strains.Result With the extending of culturing time,the long rod of germs shape has been changed into short rod then into sphero-rodlike.Germ in nucleoid is growing into thick and dim one from thin one.The second division become invisible as it changes.Lipid vocuole in cell can be found to be more,then little,A crowded of glucogon granule in germs end can be found then become invisible.There is one or three metachromatic granule growing out from nothing.Conclusion Changes in germs structure relate to medium in environment.