We studied the reproductive characteristics of the spiny lizards, Sceloporus horridus and Sceloporus spinosus (Phrynosomatidae). The specimens (N = 102) of S. horridus came from the state of Morelos and Guerrero, and individuals of S. spinosus (N = 87) came from Puebla, México. Male S. horridus exhibited a peak of reproductive activity during early spring and early summer and male S. spinosus during spring and autumn. Females of both species showed a reproductive peak during the summer. Vitellogenesis of S. horridus began in late March and of S. spinosus in late January, and ovulation in both species occurred during spring and early summer. Mean snout–vent length (SVL) of sexually mature females (based on the largest 50%) was higher in S. spinosus (x̄ ± SE = 98.6 ± 1.85) than in S. horridus (91.4 ± 1.32, P < 0.05). Mean clutch size (vitellogenic follicles oviductal eggs) for S. spinosus was higher (18.5 ± 1.5, N = 18) than for S. horridus (14.8 ± 0.91, N = 30, P < 0.05). There was no significant correlation between snout–vent length of females and clutch size of S. spinosus (r = 0.51, P > 0.05) or S. horridus (r = 0.06, P > 0.05).