Objective To evaluate ocular biometry measurements and intraocular lens （IOL） power calculation with the new optical biometry Lenstar， and to review the effect of cycloplegia on biometric parameters and IOL power calculation on patients with cataracts. Methods In this prospective， comparative， observational study of ocular measurements on 76 cataracts， measurements of axial length （AL）， corneal curvature （K1， K2）， anterior chamber depth （ACD） and white to white （WTW） were performed by a single operator using the Lenstar and the IOLMaster before and after pupil dilation. The sequence of the measurements pre- and post-cycloplegia between the two devices was randomized. Pre- and post-cycloplegic IOL power were performed with 4 formulas （Sanders-Retzlaff-Kraff/Thoretical， Holloday 1， Hoffer Q and Haigis） using an A constant of 118.0. The refractive target was post-operative emmetropia. Bland-Altman plots were applied to evaluate the agreement and differences between the two devices. The differences between pre- and post-cycloplegic measurements as well as IOL power calculations with the 2 devices were assessed using a paired t test， and their correlation was reviewed by the Pearson coefficient. Results The pre- and post-cycloplegic measurements of AL and K1 and K2 performed with both devices correlated well （Lenstar， r=1.00， 0.990， 1.00， respectively） and （IOLMaster， r=1.00， 0.99， 0.99， respectively）. ACD and WTW were significantly longer after pupil dilation： Lenstar （3.05±0.35 mm， pre-cycloplegia） vs （3.13±0.34 mm， post-cycloplegia） with ACD （t=-3.98， P<0.01） and （11.56±0.55 mm， pre-cycloplegia） vs （11.76±0.51 mm， post-cycloplegia） with VCD （t=-5.09， P<0.01）； IOLMaster， （3.03±0.34 mm， pre-cycloplegia） vs （3.15±0.34 mm， post-cycloplegia） with ACD （t=-9.00， P<0.01） and （11.85±0.44 mm， pre-cycloplegia） vs （12.15±0.47 mm， post-cycloplegia） with WTW （t=-6.52， P<0.01）. All measurements except WTW were closely related. The 95%LoAs in both devices were -1.20～0.61 mm pre-cycloplegia and -1.09～0.33 mm post-cycloplegia. The differences between pre- and post-cycloplegic IOL power were not statistically significant except for the IOLMaster using the Haigis formula （t=2.31， P<0.05）， but the values were not clinically different. Conclusion Lenstar biometry provides precise measurements and correlates well with IOLMaster， thus either can be used for the preoperative examination of cataracts.