Using unique data from goal enabling Fintech app in Australia, we document the relationship between online sports betting and investing in mutual funds at the individual level. Using past weight of each asset in a portfolio to instrument for its current asset in the portfolio, we find returns from investment lead to more gambling for most of the app users who have gambled before (complement) but lead to less gambling for serious gamblers who take a relatively high fraction of investment capital for gambling (substitute). Also, we find that the new regulation that disallowed credit lending by gambling websites and the suspension of the National Rugby League lead to less gambling but more flow into mutual fund investment. Hence, we shed light on an understanding the relationship between gambling and investment.