1 | INTRODUCTION Skin has an intact epidermis with layers that acts as a solid barrier to outside influences. It is composed of abundant components such as collagen, elastin, and glycosaminoglycans. As one grows older, the synthesis of collagen in skin reduces, especially type I and III collagen which results in uneven focal ptosis and laxity of the soft tissues around whole areas including infraorbital, buccal, mental, and submental parts.1,2 A lot of facial rejuvenation techniques were developed to reverse or delay aging process such as lasers, fillers, botulinum toxin, fat grafts, and other soft tissue augmentation procedures.3-7 Various face lift surgeries have been the traditional methods of facial rejuvenation since the early 20th century.8 However, surgical methods with incisions have some disadvantages compared to nonsurgical methods such as difficulty of the techniques, high cost, long operation time and recovery periods, and surgical scars.9 With the advent of various facial rejuvenation techniques, minimally invasive methods have gained popularity.9 Especially, the thread lift is a safe and effective technique that lifts sagging skin on the face and neck using threads that are absorbed biologically. The evolution of thread lifting procedure is now in its third decade since Sulamanidze first proposed lifting using Aptos threads.10 Sulamanidze developed the first barbed (short) suture technique using the “Aptos” thread in the late 1990s.10 In 2002, the Woffles (long) thread, also known as Waptos was developed.11 This thread was used as a suture suspension sling to lift facial soft tissues to the deep temporal fascia.11 Isse reported an endo-progressive face lift suture in 2005.12 This suture was fixed to the temporal fascia with a thread created by modifying the “Aptos” thread. Most of the techniques mentioned above involve a polypropylene thread which is nonabsorbable. Some have warned the dangers of nondegradable threads. They have a risk of migration, extruding from the skin, and may be visible under facial skin.13 Nowadays, the use of lifting threads made from biocompatible and biodegradable materials has received global attention. The absorbable threads make skin lifted immediately through mechanical effects.14 And these threads stimulate neocollagenesis process of tissues, which results in the production of new collagen.11,12 About 6 months after beginning of the implantation, the threads will degradate through hydrolysis.15 After this, synthetic absorbable thread-induced collagen synthesis will last about 2 ~ 3 months.8 There have been biodegradable thread materials such as polycaprolactone (PCL) and poly-L-lactic acids (PLLA) starting with polydioxanone (PDO).10,12,16 The PCL thread has received the most attention recently among them.15 PCL is very flexible and highly elastic substance; thus, it causes less pain and discomfort compared to PDO and PLLA. PCL is biodegradable and decomposed into CO2 and H2O. Its safety is proven from various biodegradable medical devices approved by the US Food and Drug Administration (FDA).17 Threads made from PCL are slowly absorbed into the body within 1 ~ 1.5 years compared to PDO (6 ~ 8 months) and PLLA (12 months).18 For functional improvement of the collagen synthesis and wrinkle improvement, the new PCL thread with less residual monomers and a higher molecular weight has been developed expecting prolonged durability and enhanced efficacy. There have been no other studies comparing antiaging effects on tissues of commercial threads focusing on collagen synthesis and wrinkle improvement. This study was performed to determine the efficacy of the new PCL thread compared to other commercial threads in vivo model. This preliminary study will provide guidance for future investigations.