Ternary ZnSnAs2 thin films heavily doped with nominal 10 and 20% Mn content on InP (001) substrates are grown using low-temperature molecular beam epitaxy and their magnetic and transport properties are investigated for the first time. It is found that the Mn-doped ZnSnAs2 thin films are pseudomorphically grown on nearly lattice-matched InP (001) substrates, and a trace amount of secondary phase MnAs formation is observed by high-resolution X-ray diffraction (HR-XRD) measurements. Magnetization measurements on Mn-doped ZnSnAs2 thin films reveal that the Curie temperature is around 334 K. Nominal magnetic moments per Mn atom measured from the saturation magnetization of hysteresis loops at 5 K have been estimated as 528 and 4.17 mu(B) for 10% and 20% Mn-doped ZnSnAs2 thin films, respectively. We have found from Hall effect measurements that the 10% and 20% Mn-doped ZnSnAs2 films exhibit n-type conduction, in contrast to p-type conduction in ZnSnAs2 doped with less than 10% Mn. This is likely related to the presence of a certain amount of Mn interstitials or Mn3+ substitution on Zn site in the samples. (C) 2011 Elsevier B.V. All rights reserved.