Age at puberty is an important factor in estimating the potential productivity of the bovine female. A study was conducted at the ARS-USDA Jornada Experimental Range in 2006 and 2007 to compare onset of puberty, BW, and serum insulin in Criollo and Angus-Hereford crossbred heifers. In 2006, 7 Criollo and 5 crossbred heifers were used to determine length of the estrous cycle and insulin concentrations. Heifers grazed the same pasture during the study with free access to water and mineral supplement. Blood samples were collected twice weekly for both years. In 2007, 15 Criollo and 15 crossbred heifers were used to determine age to puberty (2 or more consecutive progesterone concentrations > 1 ng/mL), length of the estrous cycle, and insulin concentrations. Initial BW in both 2006 and 2007 crossbred heifers were heavier (P < 0.01), when compared to Criollo heifers (251.7 and 166.4 ± 12.9 kg; 236.2 and 158.8 ± 4.7 kg, respectively). In 2006, BW gain did not differ (P < 0.01) between breeds (80.5 and 71.1 ± 4.4 kg for crossbred and Criollo heifers, respectively). In 2007, crossbred heifers gained more BW than Criollo heifers during the study (P < 0.01; 128.2 and 91.2 ± 4.1 kg, respectively). In 2007, BW at puberty (P < 0.01) was greater for crossbred heifers than Criollo heifers (323.8 and 213.9 ± 6.6 kg, respectively). However, Criollo heifers tended (P = 0.15) to reach puberty earlier than crossbred heifers (363.5 and 376.7 ± 6.3 d, respectively). Estrous cycle length between crossbred and Criollo heifers in both 2006 and 2007 did not differ (P > 0.53; 18 and 19 ± 1 d; 18 and 19 ± 1 d, respectively). Serum insulin concentrations were also greater (P < 0.01), for Criollo compared to crossbred heifers in both 2006 and 2007 (0.67 and 0.54 ± 0.02 ng/mL; 0.68 and 0.58 ± 0.02 ng/mL, respectively). This study suggests that Criollo heifers may reach puberty earlier than British breeds.