Schemes for converting photonic polarized‐entangled Knill–Laflamme–Milburn (KLM) states to Greenberger–Horne–Zeilinger (GHZ) states are proposed using weak cross‐Kerr nonlinearity and X‐quadrature homodyne measurement. Analyses show that the two‐qubit (Bell state) and three‐qubit conversion cases have very high fidelities and close‐to‐unity probabilities. The conversion processes are robust against photon loss. The schemes linking these two entangled states may be helpful to the study of quantum information processing based on them. Based on weak cross‐Kerr nonlinearity, theoretical schemes are presented to bridge two multiple entanglements: Knill–Laflamme–Milburn (KLM) and Greenberger–Horne–Zeilinger (GHZ) entangled states. Adopting grouping and parity measurement, the KLM entanglement is decomposed into GHZ entanglement completely. Analyses considering photon loss show that high fidelities are reached for the two‐ and three‐qubit cases.