Conventional glass/carbon fiber-reinforced polymer (G/CFRP) composites have been widely used for infrastructure applications in the past decades. Nowadays, there is a trend to use cost-effective and ductile FRP composites such as polyester FRP (PFRP). This paper presents the results of an experimental investigation on the compressive behavior of concrete confined by PFRP jackets with low strength and high ductility. Twenty-seven PFRP confined plain concrete and nine unconfined plain concretes were tested. The considered experimental variables included concrete strength and PFRP thickness. Test results indicated that the PFRP jacket confinement increased the ductility of concrete to a great extent. However, the confinement on the enhancement in concrete ultimate compressive strength is limited. In addition, some existing stress–strain models were used to predict the ultimate stress and compared with the experimental results, and new confinement models were also proposed for PFRP-confined concrete.