A string-like sealing material characterized in that (1) the string-like sealing material is a string-like body (a) obtained by forming a thermosetting resin composition comprising a synthetic resin and a heat-curing agent or a string-like composite structure (b) obtained by arranging a dimension-stabilizing aid along the lengthwise direction of the string-like body (a), (2) the elongation percentage thereof is within 10% as measured by applying a load to become stress of 5 N/cm.sup.2 per unit sectional area at 23.degree. C. for 5 minutes to the string-like sealing material in the lengthwise direction thereof, and (3) the string-like body (a) has high shape-retaining ability at normal temperature (5 to 35.degree. C.), but exhibits good melt flowability upon its heat curing.