Heat-insulating sheet and battery pack

The invention provides a heat-insulating sheet and a battery pack. The heat-insulating sheet has excellent heat-insulating properties in a large temperature range from the temperature during normal use of a battery to a high temperature of 500 DEG C or more. The heat-insulating sheet (10) contains first inorganic particles (20), second inorganic particles (21) comprising nanoparticles, first inorganic fibers (30), and second inorganic fibers (31), and the total content of the first inorganic particles (20) and the second inorganic particles (21) is 30-90 mass% with respect to the total mass of the heat-insulating sheet. The first inorganic particles (20) have a D50 of 1 [mu] m or more and 100 [mu] m or less and a D90/D10 ratio of D90 to D10 of 10 or more and 1000 or less, where D10, D50, and D90 are the particle diameters accumulated by 10%, 50%, and 90% from the small particle diameter side in a volume-based cumulative distribution of the first inorganic particles measured by a laser diffraction/scattering m