This study proposed a new design of a passive micromixer employing several J-shaped baffles in the tee channel to enhance mixing. The mixing performance of the device was investigated experimentally and by numerical simulation. The in-plane structured micromixer was fabricated using micromolding of SU-8 photoresist and PDMS. The mixing performance was demonstrated using image analysis to quantify the concentration distribution in the microchannel. The percentage of mixing increased as the number of baffles increased. The simulated and experimental results showed that the mixer with J-shaped baffles exhibited better mixing performance, and the percentage of mixing was about 1.2 to 2.2 times higher when compared to those without baffles, in the range of Reynolds number (Re) 5 to 350. The improvement in mixing performance was especially apparent at the short axial distance and at the lower Reynolds numbers. The results revealed that the J-shaped baffles could result in lateral convection in the main channel, resulting in improved mixing.