We analyzed seven Y chromosome binary markers (YAP, RPS4Y_711,;M9,;M175,;LINE1,;SRY_+465$ and 47z) in samples from a total of 254 males from Koreans and tow Mongolian ethnic groups (Buryat and Khalkh) to study the genetic relationship among these populations. We found eight distinct Y haplogroups constructed from the seven binary markers. Haplogroup DE-YAP was present at extremely low frequencies (∼2%) in the Korean and Mongolian populations. This result is consistent with earlier reports that showed the YAP+ chromosomes to be highly polymorphic only in populations from Japan and Tibet in east Asia. The observed high frequency of haplogroup $C-RPS4Y_711$ in the Mongolian populations (∼40%) is concordant with recent findings, showing that the $RPS4Y_711$-T chromosomes were distributed at high frequencies in Siberian and Mongolian populations compared with most other populations from east Asia. Thus, the relatively moderate frequency of haplogroup $C-RPS4Y_711$ in Korean (∼15%) can be seen as genetic evidence for probable interaction with Mongolian and/or Siberian populations. In contrast, the majority (∼75%) of modern Koreans studied here had high frequencies of Y chromosome lineages of haplogroup O-M175 and additional haplogroupts that define sublineage of O-M175, which are most likely related with modern populations in China. In conclusion, our data on the Y chromosome haplogroup distribution may provide evidence for interaction between Korean and Mongolian populations, but Korean tend to be much more related with those from southern-to-northern populations of China than to Mongolians in east Asia.