The present text book includes the study of influence of property variations in single- phase, laminar, forced gas micro-convection with and without entrance effect. Two-dimensional micro- sized axisymmetric geometry with constant wall heat flux boundary condition is considered to predict flow behaviour and thermal development. The steady state,continuum-based conservation equations are numerically solved to account for non-rarefaction scaling effects. Investigations have been reported on the role of variations in fluid properties on laminar micro-convection characteristics.For the case of heated air, variation in gas specific heat at constant pressure and thermal conductivity causes increase in Nusselt number. It is proposed that deviation in convection with specific heat, thermal conductivity variation is significant through temperature field than density and viscosity variation on velocity field. The non- dimensional governing equations show significance of momentum transport in radial direction due to gas viscosity variation and energy transport by fluid conduction due to thermal conductivity variation.