Designing high‐performance water‐degradable plastics is an important way to address marine microplastic pollution. A series of poly(neopentyl terephthalate‐co‐neopentyl succinate) (PNST) copolymers were synthesized using the one‐step melt‐polycondensation method. The 1H‐NMR results showed that the neopeantyl succinate (NS) and neopeantyl terephthalate (NT) segments were randomly distributed, and the Fox model indicated that they demonstrate good compatibility. The PNST copolymers showed excellent mechanical properties. The tensile strength of poly(neopentyl terephthalate) (PNT) was 50.3 MPa, and the elongation at break was 10.0%. SA segments improved the flexibility of the PNT units, and the elongation at break of PNS was 2200%, which was more than 220 times than that of the PNT copolymer. The PNST copolymer had two decomposition platforms. The fastest decomposition rate of PNS occurred at 450°C, and that of PNT at 500°C. SA units improved the rotation and hydrophilic properties of the chains, which allowed for degradation and reduced the water contact from 102.9° to 68.9°. The weight loss of PNS was more than 20% after degrading in alkaline solution for 49 days, and 1% and 1.9% in neutral and acid solution, respectively. Thus, PNST copolymers are promising water‐degradable materials with good tensile and excellent thermal properties.