When choosing a rumen-protected lysine product (RPL), not only the product efficacy but also handling stability in the practical use should be paid attention to. The 2nd generation AjiPro-L (A2G; Ajinomoto Co., Inc.) has been proven to possess higher bioavailability than the 1st generation product (A1G) based on in vivo plasma lysine technique (Whitehouse et al., 2014; Tucker et al., 2014). The objective of this study was to compare handling characteristics between A1G and A2G. A1G or A2G was mixed in a concentrate mix, and the mixing homogeneity was examined. The mix was loaded into a feed truck, transported for 160 km, unloaded into a feed bin, and was discharged. Samples were collected at the time of loading into the truck and discharging from the feed bin. The samples were sieved to separate the particles of A1G or A2G to calculate the inclusion rate. Results showed the inclusion rate of A2G remained unchanged between before and after transportation (P > 0.05) while that of A1G decreased after transportation (4.0 vs. 3.6%, P < 0.05), suggesting superior mixing homogeneity of A2G over A1G probably thanks to a smaller particle size of A2G (1 – 2 mm in diameter) than A1G (6 – 7 mm). Next, TMR mixing stability was evaluated with the same procedure as Ji et al. (2012). Dacron bags containing 1 g of RPL were mixed with TMR for 6 min in a Super Data Ranger. Then, bags were incubated in the rumen of 3 fistulated cows for 6, 12, and 24 h. After incubation, bags were washed and dried. Amounts of Lys in the residual product were analyzed for calculation of in situ protection. In situ protection of A2G mixed with TMR was slightly lower than A1G (97 vs. 99% at 6 h, 93 vs. 97% at 12 h and 85 vs. 91% at 24 h, respectively, P < 0.01). The protection of both RPLs was not affected by mechanical mixing (P > 0.05). Finally, storage stability of A2G was examined under −22 to 104°F by using the in vitro procedure (Miyazawa et al., 2014). In vitro ruminal protection or intestinal dissolution was not deteriorated at least for 6 mo under the ambient temperature tested. Results demonstrate that A2G possesses sufficient handling stability for a use under practical conditions.