To provide an electrolyte composite for a fuel cell high in oxidation resistance and low in water-absorbing property.

The electrolyte composite containing a polymer electrolyte material having a structure expressed by a general formula (1) is provided. In the general formula (1), BP is a base material composed of a polymer having a carbonaceous skeleton. R1 and R2 are each hydrogen or alkyl groups of which the structures are independently decided. R3 is a straight-chain or branching alkylene group of which the carbon number is m, p is an integer≥0, and m, n, and p are each selected from positive integers.