Stable isotope ratio of carbon and nitrogen ($delta^{13}C$ & $delta^{15}N$), and $Delta^{9}$-tetrahydrocannabinol (THC) contents were measured on 37 Korean cannabis and 10 commercial grade marijuana seized in Korea. Factors influencing on the measured values and their variations were investigated. $delta^{13}C$ value of cannabis is specified mainly by water availability. Korean cannabis showed relatively low $delta^{13}C$ values ranging -33.29$sim$-27.01% (mean=-31.01%), which reflect geographic conditions of Korea where is rainy, especially during summer. $delta^{15}N$ values, which reflect individual planting conditions, were relatively high up to -0.5$sim$18.0% (mean=6.44%). It reflects characteristics of Korean cannabis growing wild in forest or cultivated in fertile soil. Tetrahydrocannabinol is the major hallucinogenic compound of cannabis. Ethanol extracts of cannabis leaves were derivatized by N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), and the derivatives were analyzed by GC-MS in selected ion monitoring (SIM) mode. THC contents of Korean cannabis ranged 0.11$sim$4.34% (mean=1.47%), which were relatively low compared with commercial grade marijuana.