Microchannels are susceptible to blockage by solid particles. The lifetime of microfluidic devices depends on their ability to maintain flow without interruption, while certain applications require microdevices for transport of liquids containing particles. In this work, the phenomenon of interest is the formation and growth of clusters in the flow of a dilute suspension of hard spheres. Based on the present experiments, aggregation of clusters was observed for particle-laden flow in a microchannel with particle void fraction as low as 0.001 and particle diameter to channel height ratio as low as 0.1. The incipience and growth of a single cluster is discussed, and the spatial distribution and time evolution of clusters along the microchannel is presented. Although the cluster size seems to be independent of location, higher number of clusters is found at the inlet/outlet regions than in the microchannel center. Similar to individual cluster, the total cluster area in the microchannel grows almost linearly in time. The effects of flow rate, particle size and concentration are also reported.