The rapid development of digital society and artificial intelligence has triggered explosive demands for specialty plastics, especially conjugated polymers that are instrumental for flexible electronics and smart devices. The recycling and degradation of postconsumer conjugated polymers have become more important than ever to reduce the pressure to the environment. Here we report the discovery of an environmentally self-degradable conjugated polymer poly(deca-4,6-diynedioic acid), or PDDA. PDDA is stable in the dark or without oxygen when used as a functional material. However, when exposed to sunlight and air after the service life, PDDA disintegrates rapidly and fully decomposes through photooxidation in a week, yielding biocompatible, value-added succinic acid as a major degradation product. The complete degradation of PDDA into green upcycling products by sunlight in air, without leaving any microplastics, not only renders a pioneering paradigm of environmentally self-degradable conjugated polymers but also inspires developing effective strategies to completely degrade postconsumer conjugated polymers in a natural environment.