A portable gamma ray monitoring system interfaced with the Global Positioning System (GPS) was developed for measuring the gamma ray in an environment. The system can report the energy spectrum, activity and also position coordinates of latitude and longitude, by using a 8 bit microcontroller together with a palm type handheld computer model m505. The gamma ray measurement system consisted of 4 main parts.: 1). Amplifier circuit with gain setting from 500 to 1000. 2). Microcontroller controlled single channel analyzer (SCA) 3). Ratemeter circuit capable of receiving signal frequency from 0 to 100 kcps with a maximum non-linearity 0.03%. 4). A 10 bit Analog to digital converter having the DNL and INL less than + 1LSB. Tested result of the energy resolution by using developed system together with a CsI(T1) coupled with PIN photodiode was found to be 14.28% at 661.66 keV. For the GPS received only L1 frequency and used NMEA-0183 protocol for reading the position coordinates. When the position coordinates was transformed to UTM system, the errors of measuring position coordinates were found to be + 1.69 mE, -1.63 mN from the standard reference position coordinate.