Micro-light-emitting diode (micro-LED) has been widely concerned in the field of display and wireless optical communication due to its excellent optoelectronic characteristics, but the reduction of pixel size has a significant impact on the performance of GaN-based micro-LEDs and then affects the display and wireless optical communication applications. In this work, different sizes of violet and blue GaN-based micro-LEDs have been successfully fabricated, and the size-dependent characteristics of micro-LEDs in display and communication applications have been systematically studied. It can be found that the pixel size reduction of the micro-LEDs from 80 μm to 10 μm leads to an obvious decrease in light output power (LOP) by 88.30 % and 44.10 % for blue and violet micro-LEDs, respectively, and a decrease in peak external quantum efficiency (EQE) by 55.14 % and 46.25 % for blue and violet micro-LEDs, respectively. Besides, micro-LED with smaller size tends to exhibit a less obvious shift of peak wavelength and smaller broadening of full width at half maximum (FWHM) with the increases of current density, showing the potential to achieve stable display with high quality. Also, the influence of current density on chrominance coordinate migration is determined, which shows that the driving current density corresponding to the maximum EQE can promote display efficiency and color gamut. In addition, the violet and blue micro-LEDs with a diameter of 20 μm show potential in balancing between LOP and modulation bandwidth to achieve the highest data rate of 1.347 Gbps and 1.032 Gbps in wireless optical communication applications, respectively. The results in this study are of great significance for optimizing the pixel size of micro-LED to improve the performance in display and wireless optical communication applications in the future.