To provide an assist kit for insertion of a gastrostomy catheter capable of significantly reducing a burden of a patient's body by installing the gastrostomy catheter while dilating a formed hole when installing the gastrostomy catheter between the abdominal wall and the gastric wall of the patient.

An assist kit for insertion of the gastrostomy catheter used when inserting a gastrostomy catheter 10 including a bumper portion 10c and a tube portion 10b into a hole comprises a bumper cover 30 and a guide wire 37. The bumper cover 30 comprises a sheath part 31 capable of covering the bumper portion 10c, and a tapered distal dilation part 32 provided at the distal end side of the sheath part 31. The guide wire 37 comprises a wire portion 37a and a spherical portion 37b. The distal dilation part 32 includes a unidirectional passage mechanism including a groove 35b that allows the passage when the spherical portion 37b heads from the distal end side towards a rear end side, however, when heading from the rear end side towards the distal end side, being engaged therewith so as not to allow the passage.