Magnetic holes (MHs) are pressure-balanced structures characterized by distinct decreases in the interplanetary magnetic field (IMF) strength in otherwise unperturbed solar wind. In this paper we present an analysis of MHs upstream of the Martian bow shock based on three months of observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Plasma properties within and around these structures as well as their shape characteristics are examined. We find an occurrence rate of around 2.1 events per day. About 48 percent of all events are of linear type with magnetic field rotation across the hole less than 10 degrees. We observe linear magnetic holes both as isolated events and as part of a train of magnetic holes. The proton temperature anisotropy inside MHs increases while alpha particles remain mostly isotropic. The average electron temperature inside MHs modestly increases with increasing hole depth. The duration of linear holes at 1.5 AU shows an increase compared to durations at smaller heliocentric distances, but the structures remain asymmetrical and ellipsoid. A case study of MHs accompanied by a population of heavy pickup ions is also discussed.