Objective To compare the anesthetic efficacy and safety of small-dose lidocaine and ropivacaine under spinal anesthesia in ambulatory case of ureteroscopy Methods The study by the ethics committee of the hospital authority, patients signed informed consent. According to the random number table method, 100 ASAⅠ-Ⅱ patients under spinal anesthesia were randomly divided into four groups (n=25). Group L1 with lidocaine 10mg, group L2 with lidocaine 15mg, group R1 with ropivacaine 10mg, and group R2with ropivacaine 15mg. All local anaesthetics were diluted to 3ml with cerebrospinal fluid. The BP heart rate、the onset time of sensory and motor block、neurological after effect were monitored and recorded. Results After spinal anesthesia ,the BP and heart rate in groups L1 and R1 were stable, but descended in groups L2 and R2. There were no differences regarding onset of sensory block among all groups. The onset of motor block in lidocaine groups were slower and milder than that in ropivacaine groups. Lovett score in Group L1 was significantly higher than the other three groups, time course of staying in hospital, and recovery of analgesia in Group L1、L2 were significantly shorter than that of groups R1 and R2. There was no transient neurological syndrome (TNS) during follow-up. Conclusions Small-dose lidocaine spinal anesthesia can be safely applied in short operation for day surgery, because of stable circulation status, perfect the sensory block, weak motor block, short hospital stay and no neurological toxicity.