On the basis of experimental and numerical analysis, it was shown that a trapezoidal cross-section enhanced convective mixing in a zigzag microchannel. In a rectangular channel, a pair of secondary flow vortexes arranged vertically appears at high flow rates. In a trapezoidal channel, this geometrical symmetry in secondary flow pattern is broken and, as a result, convective mixing is enhanced moreover. The results of numerical simulations by the fluid particle tracer method agreed with mixing patterns obtained in experiments. An extended Danckwerts' intensity of segregation was applied to evaluate quantitatively the mixing pattern of intersection points of fluid particles with the conduit' s cross-section. This index also showed higher mixedness in a trapezoidal channel than in a rectangular one.