Hyaluronic acid (HA) is an extracellular matrix having a high molecular weight. This study is to investigate (1) whether the ultrapure HA had effect on the healing of full thickness skin wounds in animals, and (2) the relation between the effect of HA and the size of the molecular weight of HA. The ultrapure HA with different molecular weights and HA with intermediate molecular weight were applied topically to the wounds from removal of full thickness of skin and topical application of normal saline was used as control. At 21st, day after the topical application, the tensile strength was reduced in wounds of groups of HA with high and intermediate molecular weights, but not in the group of low molecular weight. Using laser-Doppler scanning of the dynamic changes of the wound perfusion, in the 3rd day the blood supply to the wound was reduced in HA groups of high and intermediate molecular weights, but at the 7th day, the blood supply of all wounds in the two groups was increased. The study revealed that HA with different molecular weights had different actions on the contraction of wounds, the angiogenesis of the granulation tissues and the healing strength of the wounds. It was indicated that hyaluronan could be used for wound treatment or as a carrier, but its accurate composition must be carefully noted.