Minimal rule generation in Non-deterministicInformation Systems (NISs), which follows rough sets based rule generation in DeterministicInformation Systems (DISs), is presented. According to certainrules and possiblerules in NISs, minimalcertain rules and minimalpossible rules are defined. Discernibilityfunctions are also introduced into NISs for generating minimal certain rules. Like minimal rule generation in DISs, the condition part of a minimal certain rule is given as a solution of an introduced discernibility function. As for generating minimal possible rules, there may be lots of discernibility functions to be solved. So, an algorithm based on an order of attributes is proposed. A tool, which generates minimal certain and minimal possible rules, has also been implemented.