The experimental results of two-phase flow boiling pressure drop of R134a in vertical microdiameter stainless steel tubes are presented in this paper. The tests were conducted using four tubes: one tube with an inner diameter of 0.52mm and 100mm heated length and three tubes with an inner diameter of 1.1mm and different heated lengths (150, 300, and 450mm). Other experimental conditions include mass flux range of 200-500kg/m(2)-s, system pressure range of 6-10 bar, inlet subcooling value of about 5K, and heat flux range of 1-140 kW/m(2). The results indicated that the total measured two-phase pressure drop increases with increasing mass flux, heat flux (exit quality) and decreasing system pressure and tube inner diameter. The test section heated length was found to have a significant effect on the measured pressure drop per metre length. The total measured two-phase pressure drop results were also compared with eighteen macro- and microscale models and correlations.