A new piezoelectric quartz crystal (PQC) sensor using molecularly imprinted polymer (MIP) as sensing material has been developed for fast and onsite determination of pirimicarb in contaminated vegetables. Three MIPs particles have been prepared by conventional bulk polymerization (MIP-B) and precipitation polymerization in either acetonitrile (MIP-P1) or chloroform (MIP-P2). MIP-P2, with uniform spherical shape and mean diameter at about 50 nm, has shown the best performance as the sensing material for PQC sensor. The sensor fabricated with MIP-P2 can achieve a steady-state response within 5 min, a very short response time as compared to MIPs-coated PQC sensor reported in the literature. The sensor developed exhibits good selectivity (low response to those pesticides with similar structures to pirimicarb, such as atrazine, carbaryl, carbofuran and aldicarb) and high sensitivity to pirimicarb with a linear working range from 5.0 x 10(-6) to 4.7 x 10(-3) mol L(-1) (following a regression equation (r=0.9988) of -DeltaF=0.552+1.79 x 10(6) C), a repeatability (R.S.D., n=5) of 4.3% and a detection limit (S/N=3, n=5) of 5 x 10(-7) mol L(-1). The MIP-coated PQC sensor developed is shown to provide a sensitive and fast method for onsite determination of pirimicarb in aqueous extract from contaminated vegetables with satisfactory recoveries from 96 to 103% and repeatability (R.S.D., n=5) from 4.6 to 7.1% at pirimicarb concentrations ranging from 8.0x10(-6) to 2.0 x 10(-4) mol L(-1).