An asymmetric-top free radical CH2CN, which as a 2B1 ground state, was detected for the first time by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11 - 10 to 14 - 13 a-type rotational transitions in the frequency region of 220 - 260 GHz, and many hyperfine resolved components for the N = 4 - 3 and 5 - 4 transitions in the 80 and 100 GHz regions, respectively. The authors assign U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1 to the N = 5 - 4, 4 - 3, 2 - 1, and 1 - 0 transitions with K-1 = 0 of the CH2CN radical.