An annual infusion of zoledronic acid (ZOL) reduces fracture risk in osteoporotic patients. Previously, we showed that a single ZOL injection inhibited changes in bone microstructure and strength in rat tibiae after ovariectomy. Here, we determined the effects of a single ZOL injection as preventive and restorative treatment on the bone microstructure and strength in lumbar and caudal vertebrae of ovariectomized (OVX) rats. Twenty-nine female 35-week-old Wistar rats were divided into four groups: SHAM-OVX (n = 9), OVX (n = 5), OVX and early ZOL (n = 8), and OVX and late ZOL (n = 7). ZOL was given once (20 µg/kg body weight s.c.) at OVX in the early ZOL group and 8 weeks later in the late ZOL group; rats were killed 16 weeks after OVX. Trabecular and cortical bone microarchitecture were measured in lumbar (L3) and caudal (Cd6) vertebrae using micro-computed tomography, and compressive mechanical properties were determined in L3 vertebrae. Compared to SHAM-OVX, OVX rats had significantly lower BV/TV; SMI, Tb.N, Tb.Sp, and Conn.D tended to be deteriorated in lumbar vertebrae, while both ZOL groups did not differ from the SHAM-OVX group. Both ZOL groups had significantly higher BV/TV than OVX; the early ZOL group also had significantly lower SMI and higher Tb.Th. OVX tended to decrease mechanical properties, while early and late ZOL treatment inhibited OVX-induced degeneration. Neither OVX nor ZOL induced changes in the trabecular microarchitecture of caudal vertebrae. In summary, in adult rats a single ZOL injection inhibited OVX-induced changes in lumbar vertebral bone microarchitecture and strength.