Extensive research in evolutionary psychology has explored the role that altruism plays in mate preference. This research aims to investigate whether altruism is desired for long-term and short-term relationships among females and males, as well as to determine potential sex differences within this preference among Thai nationals. To that end, a self-administered online Thai language-based survey was distributed for data collection; 138 Thai respondents (mean age = 22.5, SD = 4.37) completed the survey. The respondents were asked to read nine hypothetical scenarios and rate their preferences for different individuals in the scenarios for long-term and short-term relationships. In each scenario, if one person displayed high levels of altruism, another person in the same scenario would display a lower level of altruism. A 2 × 2 × 2 mixed ANOVA indicated that both men and women significantly favoured altruistic partners for long-term relationships; whereas, when displays of altruism was low, there was only a slight difference in preference for a short-term or long-term relationship. Moreover, there was no significant difference between men and women’s desirability for altruistic partners. This study provides further support for previous altruism-based research which emphasises the importance of altruism regarding long term mate selection.