Biodegradable thermogels that undergo solution-to-gel transition have been extensively investigated last decades. Due to the simple procedure for incorporating bioactive agents, they can be promising materials various biomedical applications. F127, PEG-PPG-PEG triblock copolymer, is a prototype of thermogel. However, it suffers from a short gel duration < 1 day. We have been developing a series of biodegradable thermogels including PLGA-, PCL-, PTMC-, polypeptide-based polymers to overcome the problem of F127 as a biomaterial. On the other hand, simple modification of F127 such as end-capping with short molecular moieties, multiblock strategies, and coordination polymer systems were also investigated. In this presentation, the biodegradable thermogels will be discussed from the materials viewpoint without details of applications including F127 derivatives as well as PLGA, PCL, PTMC, polypeptides, focusing on biodegradation and gel duration.