Natural convective nanofluid flows immersed in oscillating magnetic fields are simulated with a sub-continuous nondimensional lattice Boltzmann model. The effective electrical conductivity model is built including coupled effects of nanoparticle concentrations and two Knudsen numbers. Effects of directions, frequencies, and strength amplitudes of the magnetic fields are studied in wide ranges of Hartmann numbers (0:1 ≤ Ha ≤ 600) and Rayleigh numbers (10 ≤ Ra ≤ 10). To achieve higher values of cycle averaged Nusselt numbers Nu ,L, optimal magnetic directions are along or opposite from the gravity directions. Effects of the magnetic frequency f̃ are negligible, in the conduction dominating lower Rayleigh number regime of Ra < 10. In the convection dominating regime, Nu ,L increase with Ra in orders of Ra and Ra for vertical and horizontal magnetic directions, respectively, and maximum values of Nu appear at the optimal magnetic frequency of f̃ ¼ 1=5c MaðL=UÞ for all magnetic directions. With Ra as high as 10, the oscillating amplitudes of the transient wall mean Nusselt numbers Nu increase with increasing Ha ,L, but the cycle averaged Nusselt numbers Nu decrease from 9.35 to 1.42 with increasing Ha in the transient regime of 5 ≤ Ha ≤ 500. Meanwhile, heat transfer patterns transit back from convection to conduction dominating patterns with increasing Ha ,L, as illustrated by transient streamlines and isotherms.