The present invention provides an optical fiber in which transmission loss is not easily increased when the optical fiber is immersed in water and then dried and also which has a solvent resistant property and a micro-bend resistant property. An optical fiber (1) according to one embodiment of the present invention is an optical fiber (1) in which at least two layers of coating resin (3) coat the circumference of a glass optical fiber (2). When a Young's modulus of the first coating layer (31) of the coating resin (3) is defined by PY (MPa) and a water extractable rate of the coating resin (3) after immersion in 60°C hot water for 168 hours is defined by E (mass·%), a formula of 1.8 ≤ E ≤ 8.61 × PY + 1.40 is satisfied.