〔Abstract〕 Objective To investigate lim domain protein 4(LMO4) functions and mechanisms in regulating proliferation of skin squamous cells(A431), the shRNAs targeted to human LMO4 were coated by calcium phosphate nanoparticles(NP) and transfected into A431 cells to inhibit LMO4 expression. Methods Reverse transcription and quantitative polymerase chain reaction(RT-qPCR), immunohistochemistry analysis and Western blot were used to detect expression of the interest genes. The expression vectors with shRNA targeted to human LMO4(NP/sh-L) were coated by the calcium phosphate nanoparticles, and transfected into A431. The MTT assay was conducted to determine cell proliferation after transfected for 24, 36 and 48 h. Cells were stained with propidium iodide and examined cell cycles by using flow cytometry. Results LMO4 expressed at higher levels both in the skin squamous tissues and A431 cells. DNA-binding efficiency of NP/sh-L showed that the better combined ratio between calcium phosphate nanoparticles and DNA was 10 ∶1. There was no significant difference of transfection efficiency between the NP/sh-L and lipofection approaches. The MTT assay showed that silencing LMO4 inhibited proliferation of cells. RNAi-induced LMO4 inhibition exerted cell cycle arrest in G0/G1phase. Both CDK2 and cyclin E were downregulated in the A431 cells transfected with NP/sh-L comparing to the controls. However, LMO4 knockdown did not alter expression of CDK4 and cyclin D1. Conclusion The calcium phosphate nanoparticles could bind and transfer the foreign DNA into the targeted cells with high efficiency. Silencing LMO4 decreased expression of cyclin E and CDK2 resulted in inhibition of cell proliferation.