[Problems] To provide a novel alkoxysilane having a diol protected, an organosilicon resin which has a diol and the composition of which can be easily regulated, and to processes for producing these. [Means for solving problems] The alkoxysilane is an organosilicon compound represented by the following formula (1). The organosilicon resin having a diol is one obtained by hydrolyzing-condensing this compound with a multifunctional alkoxysilane. (In the formula, each of R.sub.1, R.sub.2 and R.sub.3 is an alkyl group or an alkoxy group each having carbon number from 1 to 6. R.sub.4 is an alkylene group having carbon number from 2 to 6. Z is an alkylene group having carbon number from 1 to 3.) The alkoxysilane of the present invention can be produced by a hydrosilylation reaction of a compound represented by the following formula (4) and a silane compound R.sub.1R.sub.2R.sub.3SiH. (In the formula, Z is an alkylene group having carbon number from 1 to 3 and R.sub.5 has a carbon-carbon double bond at the terminal.) The organosilicon resin of the present invention can be produced by a hydrolysis-condensation of a mixture comprising the organosilicon compound represented by the formula (1) above and a molecular weight-controlling agent.