Abstract: A ceramic substrate and a sensor element using the ceramic substrate. The ceramic substrate has a flat substrate in which an envelopment space is formed and a porous body disposed so as to cover the envelopment space. The porous body has flexibility and contact-bonding means is set to contact-bond the porous body with the flat substrate in the laminate direction. The porous body is constituted by using a woven fabric or non-woven fabric made of any one of natural fiber, synthetic fiber, and inorganic fiber so that the thickness t0 of the porous body before contact-bonded and the thickness t of the porous body 11 after contact-bonded meet the relation of 0.1t0≦t<t0. The porous body is provided with an overhanging portion to the outside of the flat substrate. The ceramic substrate prevents a fluid in the envelopment space from being replaced with bubbles even when the fluid is not sufficiently present nearby the envelopment space and there are a lot of bubbles.