Abstract: The reference Knudsen number is defined for micro gasjournal bearings and its value range is obtained according to the viscositydata of air at different temperatures. With gas rarefaction effect, modifiedReynolds equation for micro gas journal bearings is presented based onBurgdorfer's first order slip boundary condition. The finite differencemethod is used to solve the modified Reynolds equation, and pressure, loadcapacity and journal attitude angle of the bearing are obtained at differentreference Knudsen numbers, bearing numbers and journal eccentricityratios.Numerical results show that with the increase of gas rarefaction, bearingpressure and non-dimensional load capacity decrease obviously, and journalattitude angle increase. When the journal eccentricity ratio is less than0.6, journal attitude angle changes insignificantly and the influence on itfrom the reference Knudsen number is unobvious. Moreover, when the bearingnumber is small, the influence of gas rarefaction on non-dimensional loadcapacity and journal attitude angle is also insignificant.