Zailiyskiy Alatau is the most mudflow hazardous mountain region of the Republic of Kazakhstan. At the same time, this area is one of the most densely populated and economically developed one, so mudflows here cause the great damage. The paper presents results of our analysis of the glacial mudflow activity for the period from 1900 to 2019. Amount and total volume of glacial mudflows per year were used as indicators of the mudflow activity. 481 mudflows were recorded over 120 years of observations in the Zailiyskiy Alatau, and 24% of them were glacial mudflows. Glacial mudflows are the largest and most destructive. Of the nine mudflows with a volume of more than 1 million m3, seven were glacial mudflows. A chronicle of mudflow disasters is shown. From 1950 to 2019, 87 glacial mudflows were observed in the Zailiyskiy Alatau. Of these, 16 mudflows had volumes exceeding 100 thousand m3. The largest ones occurred in 1977 (6.0 million m3), 1963 (5.8 million m3), 1958 (4.0 million m3), and 1973 (3.8 million m3). Causes for formation of glacial mudflows are outbursts of moraine lakes or water from underground reservoirs, as well as collapses of moraines’ slopes. e largest of them occur when a lake is bursting through an open channel. Since 1951, occurrence of glacial mudflows has been increasing and reached its maximum in the 1970s.