Risedronate decreases osteoporotic fracture incidence; however, its effects remain unclear in elderly osteoporotic patients. Vitamin K mediates carboxylation of osteocalcin (OC), and high undercarboxylated osteocalcin (ucOC) levels indicate vitamin K deficiency and increased osteoporotic fracture risk. We aimed to evaluate the effects of risedronate alone or combined with vitamin K2 on serum ucOC, OC, and incidence of vertebral fractures in elderly osteoporotic patients. A total of 101 women with postmenopausal osteoporosis aged >60 years were randomly stratified into two groups-R group (n = 51), treated with risedronate alone; and R + K group (n = 50), treated with risedronate and vitamin K2. Serum ucOC, OC and incidence of vertebral fractures were evaluated before treatment and at 6 and 12 months post-treatment. Decreased ucOC rates at 6 and 12 months were not significant between groups. However, at 6 and 12 months, decreased OC rates in the R group (p < 0.01 and 0.05, respectively) were significantly higher than in the R + K group, and ucOC/OC change rates in the R group (p < 0.05 and 0.001, respectively) were significantly lower than in the R + K group. Vertebral fracture incidence was not significantly different between the groups at 6 and 12 months. ucOC levels in patients with incident vertebral fractures were significantly higher than in patients without incident vertebral fractures in the R group at 6 months (p < 0.05). Although no significant difference was observed for ucOC decrease rate and incidence of vertebral fractures between treatments, ucOC levels in patients with incident vertebral fractures were significantly greater than in patients without when using risedronate alone.