A steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in trapezoidal enclosures filled with water-based micropolar nanofluids is investigated numerically by using the finite difference method. The left and right inclined vertical sidewalls of the trapezoidal enclosure are maintained at the cold temperature. The horizontal top wall is considered adiabatic and moves at a uniform lid-driven velocity, while a part of the bottom wall is subjected to a uniform heat source and the remaining parts of it are considered adiabatic. An external magnetic field at different orientation angles is applied on the left sidewall of the enclosure. The fluid inside the enclosure is a water based micropolar nanofluid containing different types of solid spherical nanoparticles (Cu, Ag, Al2O3, and TiO2).Parametric studies of the influence of various parameters such as Hartmann number, Richardson number, the type of nanofluid, magnetic field orientation angle, dimensionless viscosity, dimensionless length and location of the heat source and solid volume fraction on the fluid flow and heat transfer have been performed. Comparisons with previously published numerical works are performed and good agreements between the results are observed. It is found that the average Nusselt number increases when the Richardson number decreases and the solid volume fraction increases, while it decreases as the heat source length increases. Moreover, it is observed that the Hartmann number, heat source location and the dimensionless viscosity have a significant effect on the average Nusselt number results.