Single-mode planar waveguide type UV sensor was fabricated using SU-8 and photochromic dye. Polymer waveguide was fabricated $10{mu}m$ width and $2{mu}m$ thickness for single-mode operation. The UV sensor had an absorbance with $0.0396{sim}0.114$ absorbance/mW respectively when the 5 mm sensing area was irradiated with UV for 3 sec. And sensor had a linear properties by sensing area variation. Proposed single-mode sensor had more excellent properties of UV sensitivity than other UV sensors.