Based on the SMMR and SSM/I passive microwave brightness temperature data from 1978 to 2013, we derived the variation of ice phenology in Nam Co Lake. The results indicate that the frozen period of Nam Co generally begins in January or February and ends in April or May every year; the average ice duration is [Figs. 5(a) and 5(b)]. The average freezing time is January 21. The earliest freezing time was January 4 in 1985 and 1996; the latest was February 8 in 1999, and the freezing times in 1990, 2009, and 2010 were also in February. The earliest ablation time was April 5 in 2010, and the latest was June 2 in 1986, with a difference of nearly two months. There are 16 years in which the ablation time was later than May, including seven years when the ablation time was later than May 10; six of those years were prior to 1990, and the last one was 1997. The longest duration of lake ice was 130 days, which occurred in 1986, and the shortest duration was 59 days, which occurred in 2010. Since 2000, there have been only three years when the duration of lake ice was . Between 1978 and 2000, there were only six years when the duration time of lake ice was . In the past 35 years, the freezing time of Nam Co Lake has become later by approximately 9 days on average, whereas the ablation time was advanced by approximately 9 to 10 days. The duration of lake ice has decreased by to 20 days. One point that should be noted here is, from 1978 to 2000, the average freezing time was January 19, the average ablation time was April 22, and the average duration time was 102 days. For 2000 to 2013 period, however, the average freezing time was January 23, the average ablation time was April 14, and the average duration time was 90 days.