Nowadays with increasing the terrorist threats, it is very crucial to detect any kind of explosives to provide a secure protection for important places such as; air ports, embassies, governmental buildings , public and holy places, power stations, dams, etc. Many methods have been reported to be used for detection of explosives. IMS has been proved to be one of the best methods for the detection of trace level of explosives. IMS may operate in two different modes, positive or negative. In the positive mode only positive ions are detected while in the negative mode the electric field is reversed to collect the negative ions. Explosives are commonly detected in the negative mode. Normally, an electron source is used for the ionization in the negative mode. The source utilizes a discharge in pure nitrogen which produces electrons, several orders of magnitude higher than that produced by the conventional 63 Ni. If negative corona discharge happens in air, it produces NO 2 - with a very high electron affinity, even higher than that of explosives, and prevents ionization of those compounds. Thus, negative corona discharge in air is also not appropriate for detection of explosives. The aim of this work is to use the positive corona discharge which operates in air for ionization of explosives. This was achieved by considering the pyrolysis of explosives at elevated temperature. The products of the pyrolysis contain nitrogen oxide that is well ionized in the positive corona discharge. As a result, explosives may be detected by monitoring the NO + peak in ion mobility spectrum. Moreover, each explosive show additional peaks that may be used for identification. In this thesis, thermal decomposition products of several explosives including Pentaerythritol Tetranitrate (PETN), Cyclo-1,3,5-Trimethylene-2,4,6-Trinitramine (RDX), 2,4,6-Trinitrotoluene (TNT), 2,4-Dihydro-5-nitro-3H-1,2,4-triazol-3-one (NTO), 1,3,5,7- tetranitro-1,3,5,7-tetrazocine (HMX), has been evaluate between 150ْ C to 250ْ C in positive polarity in air. The limit of detection for RDX, HMX, PETN, NTO and TNT were , 1×10 -9 , 1×10 -8 ,1×10 -6 , 1×10 -6 and 4×10 -8 g, Respectively. In continue, the new design has been use for improvement in NO + peak detection producted of the pyrolysis of explosives correct structure corona discharge. This design consists of a curtain plate to prevent the diffusion of NO x into the ionization region.Detection of explosives has been evaluate in air too. Envuronment interference (vapor and NH3) has been investigated in this condition.