Essential amino acids such as lysine are deficient in most ingredients fed to cows. Direct supplementation of lysine in cow diets however is questionable because the residence time of diets in the rumen is as long as 12 h and lysine can be hydrolyzed by some rumen microorganisms. Safe rumen delivery systems are therefore highly demanded to utilize essential amino acids. The objective of the present work was to study solid/oil/water (S/O/W) emulsions as a potential rumen delivery system that can release most lysine post-rumen. Spray-dried lysine solid particles were prepared and were suspended in soybean oil. The S/O suspension was emulsified in neutral aqueous suspensions with 2, 10, and 30% whey protein concentration (WPC), which was then acidified to pH 3.0 and mixed with a 0.5% sodium alginate solution at pH 2.0 to prepare double-layered emulsion droplets. The emulsion was then spray-dried. The dimension and morphology of droplets were studied using a laser diffraction particle size analyzer, optical microscopy, and scanning electron microscopy. The amount of unencapsulated lysine and the amount of lysine released from spray-dried powder after incubation in simulated rumen, abomasum, and intestinal juices at 37°C were determined using high performance liquid chromatography. All experiments were carried out at least in triplicate. ANOVA was carried out to determine significant differences between treatments at a significance level of 0.05. Results showed that increasing WPC concentration significantly (P < 0.05) improved the encapsulation efficiency of lysine, up to 78.5% for the 30% WPC treatment. The particle dimension was around 10 µm based on particle size analysis and microscopy. About 10% lysine was released after 12-h incubation in the simulated rumen juice containing proteases. After an additional 3-h incubation in the simulated abomasum juice at pH 2 with pepsin, the cumulatively released lysine was less than 18%. After further in vitro digestion in the simulated intestinal juice at pH 7.0 with pancreatin, pepsin, and bile salt, the cumulatively released lysine was up to 56%. Therefore, the S/O/W emulsion can be developed as delivery systems to release most lysine post-rumen to supply important amino acids for cows.