Objective. To study if the novel threadlike structure (NTS) was caused by coagulation during injecting urethane intraperitoneally and the source of NTS. Methods. Twenty-two SD rats were anaesthetized by urethane injected intraperitoneally. Heparin was injected at 5 minutes before the anaesthesia from femoral vein in 11 rats, and saline was given in the other 11 rats randomly. Six Chinese minipigs were carried to look for NTS. One sample was taken to be stained by DAPI/Phalloidin and observed by a laser scanning confocal microscope. Results. In the group of heparin, 10 rats were found to have NTS with appearance rate of 90.9%, and 9 rats were found to have NTS with the appearance rate of 80.1%. Both groups have 1.81 average numbers of NTS in each rat without significant difference (P > 0.05). In the observation of pigs, the NTS was found to prolong from the serous membranes of abdominal wall and organ surface. Histological observation showed elongated nuclei and alignment which is similar to the characteristics of PVS. Conclusion. There is no strong evidence to say that the NTS on organ surface was caused by coagulation of blood. The source of NTS might be a prolonged structure from serous membrane in abdominal cavity during the development and more or less retained after birth.