The Yukjin dialect (Yukjin Korean: 뉴웁말; Hanja: 六鎭말; RR: Nyuummal) is a variety of Korean or a separate Koreanic language spoken in the historic Yukjin region of northeastern Korea, south of the Tumen River. Its phonology and lexicon are unusually conservative, preserving many Middle Korean forms. Thus, Alexander Vovin classified it as a distinct language.

Yukjin speakers currently live not only in the Tumen River homeland, now part of North Korea, but also in the Korean diaspora in Northeast China and Central Asia that formed in the nineteenth and twentieth centuries. The dialect is under pressure from the Gyeonggi ("Seoul") dialect, the prestige dialect, as well as local Chinese and Central Asian languages.

The Sino-Korean term 六鎭 ryukchin 'six garrisons' refers to the six towns of Hoeryŏng, Chongsŏng, Onsŏng, Kyŏngwŏn, Kyŏnghŭng, and Puryŏng, all located south of a bend of the Tumen River. The area of these towns belonged to the Tungusic-speaking Jurchen people until the early fifteenth century, when King Sejong conquered the area into Korea's Hamgyong Province and peopled the six towns with immigrants from southeastern Korea. The Yukjin dialect is the distinctive Koreanic variety spoken by their descendants.

The Yukjin dialect of the six towns is further divided into an eastern variety, typified by the speech of Onsŏng and Kyŏngwŏn, and a western variety as spoken in Hoeryŏng and Chongsŏng. The eastern variety preserves more phonological archaisms. Some analyses consider the language of Kyŏnghŭng and Puryŏng to belong to the mainstream Hamgyong dialect rather than to Yukjin.

Yukjin is divergent from the dialect prevalent in the rest of Hamgyŏng Province, called the Hamgyŏng dialect, and generally more closely aligned with the western Pyongan dialect. Some of the earliest descriptions of Hamgyŏng dialects—from the seventeenth century—already noted that the speech of the Yukjin area was different from that of the rest of Hamgyŏng. The 1693 provincial gazette Bukgwan-ji stated that while most of Hamgyŏng had a "most divergent" dialect, the Yukjin area had "no provincial speech" of its own because it had been settled by people from the southern provinces, who continued to use the standard southern dialects. In 1773, the high-ranking official Yu Ui-yang also wrote that the language of Yukjin was easier to understand than southern Hamgyŏng dialects because it was more similar to southern varieties of Korean, although he conceded that "when I first heard it, it was difficult to understand".

Despite these previous similarities to southern dialects, Yukjin has now become the most conservative mainland variety of Korean because it was not subject to many of the Early Modern phonological shifts that produced the modern mainland dialects. The Hamgyŏng dialect, which participated in these shifts, now resembles the southern dialects to a greater extent than does Yukjin.

In response to poor harvests in the 1860s, Yukjin speakers began emigrating to the southern part of Primorsky Krai in the Russian Far East. Their speech was recorded in a dictionary compiled in 1874 by Mikhail Putsillo, and in materials compiled in 1904 by native speakers who were students at the Kazan Teacher's Seminary. Larger waves of immigrants from other parts of North Hamgyŏng arrived in the area in the 1910s and 1920s, fleeing the Japanese annexation of Korea.

In the 1930s, Stalin ordered the forced resettlement of the entire Korean population of the Russian Far East, some 250,000 people. The main destinations were concentrated particularly in what is now Uzbekistan and Kazakhstan. There are small Korean communities scattered throughout Central Asia maintaining forms of Korean known collectively as Koryo-mar, but their language is under severe pressure from local languages and Gyeonggi (Seoul) Korean.