While Bitcoin gains increasing popularity in different payment scenarios,the transaction fees make it difficult to be applied to micropayment.Given the wide applicability of micropayment,it is crucial for all cryptocurrencies including Bitcoin to provide effective support therein.In light of this,a number of low-cost micropayment schemes for Bitcoin have been proposed recently to reduce micropayment costs.Existing schemes,however,suffer from drawbacks such as high computation cost,inflexible payment value,and possibly unfair exchanges.The paper proposes two new micropayment schemes,namely the basic MicroBTC and the advanced MicroBTC,for Bitcoin by integrating the hash chain technique into cryptocurrency transactions.The basic MicroBTC realizes micropayment by exposing hash pre-images on the hash chain one by one,and it can also make arbitrary micropayments by exposing multiple hash pre-images.We further design the advanced MicroBTC to achieve non-interactive refund and efficient hash chain verification.We analyze the complexity and security of the both MicroBTC schemes and implement them using the Bitcoin source code.Extensive experiments were conducted to validate their performance,and the result showed that a micropayment session can be processed within about 18 ms for the basic MicroBTC and 9 ms for the advanced MicroBTC on a laptop.Both schemes enjoy great efficiency in computation and flexibility in micropayments,and they also achieve faess for both the payer and the payee.