Ammonia decomposition is a promising approach for on-site hydrogen generation for fuel cells, and the development of a cost-effective and efficient catalyst is highly desired. In this study, a series of Ni_xMg_75-xAl₂₅ hydrotalcite-like compounds (HTlc) with different Ni contents were synthesized by co-precipitation, followed by calcination and reduction treatments. Influences of Ni content and ammonia reduction on the catalytic performance for ammonia decomposition were investigated. The characterization results of the as-prepared samples showed that HTlc was decomposed into Mg(Ni, Al)O solid solution by calcination, which displayed a strong interaction between Ni species and support, while upon reduction with ammonia at 750 ℃, well-dispersed Ni metal nanoparticles with an average crystallite size range of 5.9-7.7 nm were formed. No nitrogen oxides (NO_x) were produced during the NH₃ reduction process as indicated by mass spectrometry analysis, and the catalyst reduced with ammonia showed comparable activity with that reduced with hydrogen, suggesting that ammonia can be used as a reductant gas. The catalyst activity increased with the increase of Ni content and reduction temperature. Among the catalysts, the Ni₂₀Mg₅₅Al₂₅ catalyst reduced with ammonia at 750 ℃ showed the best activity, which afforded 98% ammonia conversion at 600 ℃ at a space velocity of 30000 mL·g_cat^-1·h^-1, and no evident deactivation was observed during a 100 h test, demonstrating good activity, stability, and sintering resistance.