A yarn which is prepared by doubling polytrimethylene terephthalate fibers, in particular, polytrimethylene terephthalate multifilament fibers having a single yarn fiber fineness of 1 to 56 dtex, and has a total fineness of 2000 to 22000 dtex; a gut comprising a yarn which is prepared by doubling polytrimethylene terephthalate multifilament fibers having a single fiber fineness of 1 to 56 dtex and has a total fineness of 7000 to 22000 dtex; and a string for a musical instrument comprising a yarn which is prepared by doubling polytrimethylene terephthalate multifilament fibers having a single fiber fineness of 1 to 56 dtex and has a total fineness of 2000 to 14000 dtex. The yarn has high strength and a high ratio for the recovery of elasticity and the retention of stress, and is excellent in water resistance, softness and homogeneity. The gut can be stretched on a frame of a racket for tennis or the like, exhibits high rebound resilience when stretched, and retains satisfactory rebound resilience for a long period of time, and further is excellent in impact resistance, durability, and water resistance. The string for a musical instrument shows a reduced change of interval due to the elapse of time and the change of humidity and is excellent in tuning characteristics.