Ordered B2 AlNi nanoparticles are less explored, both theoretically and experimentally compared to other ordered alloy nanoparticles. Hence, comprehensive structural analysis has been carried out for AlNi nanoparticles with B2 structure generated using freezing simulations. The structural analysis in ordered B2 Al x Ni 1-x alloy nanoparticles was carried out for four concentrations: x = 0.55, 0.50, 0.45, and 0.40. The final structures show a variety of defects such as vacancies, antisites, grain boundaries and antiphase boundaries. All the grain boundaries are twin grain boundaries with misorientation very close to ∑ = 3,<110>{112} symmetric tilt grain boundary. The {100} surfaces are Al-terminated as they have low surface energy. Finally, the influence of nanoparticle concentration on the structure was studied. Al segregates to the surface resulting in a depletion in the bulk volume. This segregation progressively decreases with increasing amount of Ni in the nanoparticle. As a result, Al Ni antisites were observed at the surfaces of Al-rich nanoparticles. The {100} and {110} surfaces exhibit expansion which is not dependent on the concentration of nanoparticles. In contrast, the atoms in the bulk volume experience compression as the amount of Ni increases. The results show that structural control of ordered alloy nanoparticles that exhibit a wide range of phase stability can be achieved by varying concentration. © 2019 Elsevier Ltd