BACKGROUND: CT-guided needle biopsy of lung nodules requires breath holding during needle placement, and is thus inapplicable to patients with difficulty in holding breath. METHODS: A robotic needle biopsy technique is introduced, adapting to the patient respiratory pattern and using a robot manipulator to drive the needle towards a moving lung nodule. Based on the nodule respiratory motion model, needle placement is planned to follow an optimal timing and path, and is triggered based on the respiratory phase tracking. An experimental system has been created to study robotic needle placement. RESULTS: Preliminary phantom tests were conducted based on three representative clinically-collected lung nodule motion paths, using an 18-gauge coaxial needle set. 300 needle paths were implemented. Robotic needle driving was accomplished within 0.4 s (a typical respiratory phase), and resulted in a needle placement accuracy of 0.5 mm with a standard deviation about 0.1 mm over the non-resistance paths. CONCLUSION: The proposed robotic needle placement technique is promising for accurately biopsying lung nodules under respiratory motion and those with very small sizes.