Since durian has specific properties such as big peel, non-uniform shape, rough skin, etc. the nondestructive maturity determination is hard to perform. This paper proposes microwave free-space measurement by using 2 waveguide antennas as transmitter and receiver operating in frequency range of 2-3 GHz to determine the insertion loss (S/sub 21/) after passing through durian which can be calculated in term of complex permittivity, the results are compared with percentage dry-weight as an standard durian maturity determination. The results show that this technique can provide fast durian maturity determination with 90% accuracy.