The invention relates to a mating detection marker pen for cows. The pen can be used for detecting whether the cows are in oestrus (mate) or not. The mating detection marker pen is composed of a body marker part, an externally-wrapped envelope part and an outer layer packaging part. The body market part is prepared from an appropriate amount of pigment, castor oil, petroleum jelly, palm oil, paraffin, beewax, Fischer-Tropsch wax, kaolin, calcium carbonate, linseed oil, propyl paraben and butyl paraben. The externally-wrapped envelope part is prepared from an appropriate amount of propyl benzene emulsion, polyvinyl acetate resin emulsion, pigment, glycerol and kaolin. The mating detection marker pen for the cows is prepared through an apt technology, the marker pen coats colors on the tail portions, capable of being mounted easily, of the cows, whether colored tapes are erased or not is observed every day, and accordingly whether the cows are in oestrus or not can be judged. The marker pen has the advantages of being short in time, durable, economical, effective, free of poison, easy to distinguish, resistant to environment temperature difference, and conducive to improving the economic benefits and social benefits of the cow rearing industry.