An experimental investigation was conducted on the laminar flow frictional characteristics of suspensions with microencapsulated phase change material (MEPCM) in water flowing through rectangular copper minichannels. The MEPCM was provided at an average particle size of 4.97 μm, and was mixed with distilled water to form suspen- sions with various mass concentrations ranging from 0 to 20%. The experiment was per- formed to explore the effect of MEPCM mass concentration on friction factor and pressure drop in the minichannels. The Reynolds number ranged from 200 to 2000 to provide laminar and transitional flows. It was found that the experimental data for the suspensions with 0 and 5% concentration agree well with the existing theoretical data for an incom- pressible, fully developed, laminar Newtonian flow. For the suspensions with mass con- centrations higher than 10%, there is an obvious increase in friction factor and pressure drop in comparison with laminar Newtonian flow. An experimental investigation was conducted on laminar flow frictional characteristics of suspensions with microencapsulated phase change material (MEPCM) in water flowing through rectangular copper minichannels. The MEPCM was provided at an average particle size of 4.97 μm, and was mixed with distilled water to form suspen-sions with various mass concentrations ranging from 0 to 20%. The experiment was per- formed to explore the effect of MEPCM mass concentration on friction factor and pressure drop in the minichannels. The Reynolds number ranged from 200 to 2000 to provide laminar and transitional flows. It was found that the experimental data for suspensions with 0 and 5% concentration agree well with the existing theoretical data for an incom- pressible, fully developed, laminar Newtonian flow. For the suspensions with mass con- centrations higher than 10 %, there is an obvious increase in friction factor and pressure drop in comparison with laminar Newtonian flow.