Ultra-High Performance Liquid chromatography-electrospray ionization tandem mass spectrometry andspectrophotometry was developed for the determination of L-carnitinein milk and dairy products. A C8column( 3. 5μm,50 × 2. 1 mm) was used for liquid chromatography,with mobile phases consisting of 0. 1% heptafluorobutyric acid in water and methanol. L-Carnitine-d3 was a stable isotope internal standard( ISTD),which helped to normalize signal suppression and matrix effects. Spectrophotometry used perchloric acid to precipitate protein,alkaline saponification was used to separate free combined L-carnitine. After enzymatic reaction,spectrophotometer can detect the content of L-carnitine. The results of spectrophotometry showed that the limit of detection was 2. 0 mg /100 g,the recovery was 96. 2% ~ 104. 7%,relative standard deviation( RSD) was1. 34% ~ 3. 69%. The results of UPLC-MS /MS showed that the limit of detection was 2 ng /100 g,recovery was 97. 8% ~ 109%,relative standard deviation( RSD) was1. 77% ~5. 65%. The two methods are suitable for analysis of L-carnitine in milk and dairy products,and the results had no significant difference. UPLC /MS /MS method was simple operation,rapid,efficient,controllable. It is suit for rapid、large amount of samples detection.