Household solid waste management is widely accepted as a key indicator in measuring both the quality of life of dwellers and urban sustainability. China has recently experienced a dramatic increase in domestic waste production at the rate of 8%-10% per year1 – approaching an alarming level that poses a severe threat to the environment and citizens’ living standards. As one of the major strategies adopted in many countries, promoting source-separation of household waste to increase recycling and lighten the load of landfill and incineration (Stoeva and Alriksson, 2017), has become one of the most pressing issues on Chinese government agenda. In particular, the State Council has issued its Implementation Program of Household Garbage System in March 2017, highlighting the urgency and importance of this work. Undoubtedly, the widespread participation of general public is the key to the success of waste separation in a society, since it requires a concerted effort of social members. Like other prosocial behaviors, however, such collective action is vulnerable to the free-rider problem (Olson, 1965) and easily ends in failure. By its nature, waste separation is a voluntary provision of such public goods as a cleaner environment and more efficient utilization of energy resources (Yau, 2010), yet these longer-term and collective benefits may not cover the time, energy and/or other costs paid by individuals for accurately separating (GarcÉS et al., 2002). Moreover, they need to be supplied jointly but not excludable to anyone (Yau, 2010). Driven by rationality, hence, residents seeking utility maximization tend to free ride on others’ efforts and choose not to engage in waste separation. While collective-action problem, or ‘‘tragedy of commons” (Hardin, 1968), seems inevitable under this rational egoist assumption, it can be solved through several well-designed institutions or behavioral interventions that increase individuals’ objective payoff or motivation and hence facilitate altruistic behaviors (Ostrom, 2000). From the perspective of environmental collectivism that is seldom discussed by domestic waste separation or recycling literature (Yau, 2010), the aim of this intervention study was to compare economic incentive and social influence, which are acknowledged as two effective solutions to collective dilemma (Olson, 1965; Ostrom, 1990), in terms of their effects at promoting waste separation. We further investigated a range of psychological and socio-demographic factors that were expected to mediate or moderate these intervention effects, since it is helpful to better understand the mechanisms and scopes of such initiatives. Nonetheless, these factors are severely neglected by existing intervention-oriented studies within the domain of waste separation (Varotto and Spagnolli, 2017).