We present real-time, rapid detection of Mycoplasma pneumonia in PBS inside a Y-channel PDMS microfluidic device via optical fiber monitoring of latex immunoagglutination. The latex immunoagglutination assay was performed with serially diluted M. pneumonia solutions using highly carboxylated polystyrene particles of 390 and 500 nm diameter conjugated with monoclonal anti-M. pneumonia. Proximity optical fibers were located around the viewing cell of the device, which were used to measure the increase in 45 degrees forward light scattering of the aggregated particles. The detection limit are slightly less than 50 pg m L-1 both for 390 and 500 nm microspheres and the detection time do not exceed 90 s.