A method of reversed phase high performance liquid chromatog. for the determination of trans-vitamin K1 in health products was established.The sample (0.25 g) was weighted after grinding the vitamin K1 supplement tablets into powder, and then dissolved and made its volume up to 50 mL brown volumetric flask by isopropanol.The supernatant was filtered by a 0.45μm filter membrane and separated on a Ph column with the mixtures of methanol and 50 mmol·L-1 acetic acid solution at different volume ratios as mobile phase for gradient elution.The results showed that under the above chromatog. conditions, the resolution (RS) of cis- and trans-vitamin K1 was 1.76, linearity ranges were 0.01-2 mg·L-1 and 0.04-8 mg·L-1, with detection limits (3S/N) of 0.032 mg·L-1 and 0.074 mg·L-1, resp.Recovery test was made by adding standard solution on blank samples at 3 concentration levels, giving values of recovery of trans-vitamin K1 and cis-vitamin K1 in the ranges of 92.0%-95.2% and 90.0%-101%, and intra-day RSDs (n=6) of the determined values were in the ranges of 1.6%-2.2% for trans-vitamin K1 and 1.4%-2.3% for cis-vitamin K1.The inter-day RSDs (n=5) of the determined values ranged from 2.4% to 4.8% for trans-vitamin K1 and from 2.6% to 4.6% for cis-vitamin K1.The proposed method was used for the anal. of actual samples, and the detection amount of trans-vitamin K1 was in the range of 75.36-80.12μg·g-1.