Langmuir probe is one of the fundamental techniques for measuring properties of the plasmas. However, the problem of probe contamination makes it difficult to apply its original version directly to space plasmas. We have developed two different types of plasma probes that suffer less contamination effect. One is the modified Langmuir probe in which the pluse modulation is applied to the sweep. The second type is the electron temperature probe which consists of a pair of two sensors, one of which is modulated with a small rf signal and the change in the floating potential is monitored against the other sensor. We tested these probes using low temperature and low density plasmas generated in a large vacuum chamber. The results of test show that these probes substantially reduce the time variance of electrode surface conditions which often causes hysterisis in the Langmuir probe current-voltage characteristics.