An insurance company is required to prepare a certain amount of money, called reserve, as a mean to pay its policy holders claims in the future. There are several types of reserve, one of them is IBNR reserve, for which the payments are made not in the same calendar year as the events that trigger the claims. Wuthrich and Merz (2015) developed a Bayesian Chain Ladder method for gamma distribution that applies the Bayesian Theory into the usual Chain Ladder Method . In this article, we modify the previous Bayesian Chain Ladder for half-normal distribution, as such distribution is more well suited for lighter tail claims.