In the present study, the flow fields around a rotating blade in low-Reynolds-number condition for the Mars helicopter were visualized. Two types of optical measurement techniques were developed and implemented for the tests inside a low-pressure chambers: One is a lifetime-based pressure-sensitive-paint (PSP) measurement technique and the other is a sublimation visualization technique. The principles of these two methods are presented and the results of calibration tests are summarized. For the lifetime-based PSP method, three different types of PSP were evaluated to find the one most suitable in low-pressure applications and the optimum gate time settings for the lifetime-imaging were determined. A test model for the chamber test was a 0.3-meter-diameter rotor system with two rectangular blades of the aspect ratio of two. Tests were conducted at rotational speed of 2400 rpm and at ambient pressure of 10 kPa. Pitch angle of the blades were set to be 0, 5, 10 and 20 deg. Both methods successfully illustrated clear images of mostly pressure and skin-friction distribution on the upper surface of the blade. These images show that the leading-edge vortex is generated and covers a large part of the blade. A variation on the flow field with the blade pitch angle is also presented.