Household wealth held in private businesses supports both family finance and production. We study how relationship dissolution and property-division rules affect these businesses using Canadian administrative data linking couples, firm ownership, individual tax returns, and corporate balance sheets. A matched event study of couples who jointly own a business shows that separation shifts ownership toward male partners and away from female partners. Firms experience large and persistent declines in assets, employment, profits, and corporate tax liabilities. Male partners' personal income and tax liabilities rise, while female partners' fall. Comparing jointly owned businesses with solely owned businesses across legal married and common-law couples, we find larger contractions where partners have stronger claims on business wealth, consistent with asset division contributing to firm contraction. We then exploit British Columbia's 2013 expansion of equal property-division rights to common-law partners. The reform produces a small but noisy decline in separation rates, alongside increases in firm size and performance. Together, our findings suggest that dividing business wealth upon separation can constrain production and shift income across corporate and personal tax bases. Family law therefore has effects that reach beyond the household as it changes not only the allocation of household wealth but also the scale and performance of private businesses.