Optogenetics is a fast growing neuromodulation method, which can remotely manipulate the specific activities of genetically-targeted neural cells and associated biological behaviors with millisecond temporal precision through light illumination. Application of optogenetics in neuroscience studies has created an increased need for the development of light sources and the instruments for light delivery. Currently, laser-coupled optical fibers have been most commonly used, but the tethered optical fibers can restrict the natural behavior of the subjects while performing optical stimulations with freely moving animals. Alternatively, micro-light-emitting diodes (μ-LEDs) are power-efficient, low-cost and suitable for integration with wireless electronics. However, the wide irradiation angle and low out-coupling efficiency of LEDs significantly weaken the emitted light intensity and limit their applications for optical stimulation in deep brain regions. In this paper, we present a micro-lens-coupled LED neural stimulator with improved light out-coupling efficiency for optogenetic neuromodulation. A backside reflector and a frontside microlens are integrated with the μ-LED chip for the light collection and collimation. Microfabrication techniques are developed to construct microlens arrays on mechanically flexible substrates. The functionality of the fabricated LED stimulators is demonstrated by both numerical simulation and measurement.