In order to explore the function of β-carotene-15, 15′-monooxygenase 1 (BCMO1) in vitamin A (VA) metabolic balance in Yak (Bos mutus), the expression levels of BCMO1 protein were studied in Yak tissues at different nutrition periods. Three healthy adult males of 3 years old were selected for samples collection at July 2013 (nutrition-rich period) and March 2014 (nutrition-deficiency period) at Tongpu town of Wulan County in Qinghai Province. Western blotting were used to detect the expression of BCMO1 protein in eight tissues including liver, lung, kidney, muscle, duodenum, ileum, jejunum and rumen. The different expression levels of BCMO1 protein in different tissues at the same nutrition stage was compared using multiple comparisons and the difference of the expression level at different nutrition periods for the same tissue was compared using T test. As shown in Fig. 1 and Fig. 2, there was the highest expression level of BCMO1 protein in duodenum among all tissues (P < 0.05), and the expression level in ileum and jejunum tissue was higher than that of kidney and rumen (P < 0.05). BCMO1 protein expression level was the lowest in liver among all tissues during the nutrition-deficiency period. During the nutrient-rich period, liver tissue showed the highest level of BCMO1 protein among all tissues (P < 0.05). As shown in Fig. 2 and Table 1, the expression of BCMO1 protein in the liver was 0.919 ± 0.228 at nutrition-rich period, which was significantly higher than that at nutrient-deficiency period (P < 0.05). However, the expression levels of BCMO1 protein in duodenum, jejunum, kidney, muscle and rumen were 0.811 ± 0.134, 0.336 ± 0.255, 0.739 ± 0.404, 0.619 ± 0.092 respectively at nutrition-rich period, which were lower than those at nutrition-deficiency period (P < 0.05). The BCMO1 expression levels in lung were 1.128 ± 0.407 and 1.083 ± 0.232, and its expression levels in ileum were 0.466 ± 0.337 and 0.517 ± 0.280 at nutrition-rich and nutrition-deficiency periods, respectively. There was no significant difference between two different nutritional periods for BCMO1 expression in two tissues (P > 0.05). The expression of BCMO1 protein was lower at nutrition-rich period than that at the nutrition-deficiency period for most tissues, which indicated that sufficient content of vitamin A in tissues might inhibit expression of BCMO1, as the contents of β-carotene and vitamin A were adequate in Yak tissues at nutrition-rich time. It is very important to maintain and regulate vitamin A metabolic balance in Yak at different nutrition periods.