With the rapid advancement of quantum computing, conventional cryptographic schemes used in blockchain networks—such as ECDSA and RSA—face significant vulnerabilities. This research investigates quantum threats to blockchain security and evaluates post-quantum cryptographic (PQC) algorithms for their suitability in decentralized applications. Our methodology includes a comprehensive threat analysis, followed by simulations comparing PQC algorithms (e.g., Dilithium, Falcon, Rainbow, and SPHINCS+) against classical cryptography in key generation, signing, and verification operations. The results indicate that lattice-based PQC schemes, particularly Dilithium and Falcon, provide the best balance between security and computational overhead. While PQC integration introduces some performance trade-offs, it is essential for ensuring long-term security in blockchain networks in the post-quantum era.