Here we present the development of self-regulated “breathing” polymersome nanoreactors that show temporally programmable biocatalysis induced by a chemical fuel. pH-sensitive polymersomes loaded with horseradish peroxidase (HRP) and urease were developed. Addition of an acidic urea solution (“fuel”) endowed the polymersomes with a transient size increase and permeability enhancement, driving a temporal “ON” state of the HRP enzymatic catalysis; subsequent depletion of fuel led to shrinking of the polymersomes, resulting in the catalytic “OFF” state. Moreover, the nonequilibrium nanoreactors could be reinitiated several cycles as long as fuel was supplied. This feedback-induced temporal control of catalytic activity in polymersome nanoreactors provides a platform for functional nonequilibrium systems as well as for artificial organelles with precisely controlled adaptivity.