A solar heat pipe collector was designed and fabricated to study its performance of the outdoor test condition. The thermal performance of the wickless heat pipe solar collector was investigated for pure water and nanofluid with varied range of CNT nanofluid concentration (0.15%, 0.45%, 0.60%, and 1% by volume) and various tilt angles (20 deg, 32 deg, 40 deg, 50 deg, and 60 deg). CNT nanoparticles with diameter 10–12 nm and 0.1–10 μm length are used in the present experimental investigation. The optimal value of CNT nanofluid concentration for better performance is obtained from the investigation. The thermal performance of the heat pipe solar collector with CNT nanofluid is compared to that of pure water.