A rubber composition for a tire, comprising: a rubber component; a silica; and a silane coupling agent; the rubber component containing a specific conjugated diene rubber and a specific butadiene rubber, in the rubber component, a content of the specific conjugated diene rubber being 35 mass% or more and a content of the specific butadiene rubber being 15 mass% or more, the specific conjugated diene rubber being a conjugated diene rubber comprising a polymer block containing an isoprene monomer unit and a polymer block containing a 1,3-butadiene monomer unit and having a modified structure by a siloxane compound at least at one terminal, in the specific conjugated diene rubber: at least one of the polymer block and the polymer block containing a unit of a vinyl compound containing a functional group interactable with a silica; the polymer block having a weight average molecular weight (Mw) in a range of from 1000 to 30000, and an entire weight average molecular weight (Mw) in a range of from 50000 to 5000000; an entire aromatic vinyl monomer unit content being from 30 to 45 mass%; and an entire vinyl bond content being from 15 to 35 mass%, the specific butadiene rubber being a butadiene rubber having a glass transition temperature of -85°C or less, wherein the glass transition temperature is measured by using a differential scanning calorimeter at a temperature elevation speed of 10 °C/min and calculated based on the midpoint method, a content of the silica being from 50 to 150 parts by mass per 100 parts by mass of the rubber component, and a content of the silane coupling agent being from 3 to 30 mass% with respect to the content of the silica. a rubber component; a silica; and a silane coupling agent; the rubber component containing a specific conjugated diene rubber and a specific butadiene rubber, in the rubber component, a content of the specific conjugated diene rubber being 35 mass% or more and a content of the specific butadiene rubber being 15 mass% or more, the specific conjugated diene rubber being a conjugated diene rubber comprising a polymer block containing an isoprene monomer unit and a polymer block containing a 1,3-butadiene monomer unit and having a modified structure by a siloxane compound at least at one terminal, in the specific conjugated diene rubber: at least one of the polymer block and the polymer block containing a unit of a vinyl compound containing a functional group interactable with a silica; the polymer block having a weight average molecular weight (Mw) in a range of from 1000 to 30000, and an entire weight average molecular weight (Mw) in a range of from 50000 to 5000000; an entire aromatic vinyl monomer unit content being from 30 to 45 mass%; and an entire vinyl bond content being from 15 to 35 mass%, the specific butadiene rubber being a butadiene rubber having a glass transition temperature of -85°C or less, wherein the glass transition temperature is measured by using a differential scanning calorimeter at a temperature elevation speed of 10 °C/min and calculated based on the midpoint method, a content of the silica being from 50 to 150 parts by mass per 100 parts by mass of the rubber component, and a content of the silane coupling agent being from 3 to 30 mass% with respect to the content of the silica. at least one of the polymer block and the polymer block containing a unit of a vinyl compound containing a functional group interactable with a silica; the polymer block having a weight average molecular weight (Mw) in a range of from 1000 to 30000, and an entire weight average molecular weight (Mw) in a range of from 50000 to 5000000; an entire aromatic vinyl monomer unit content being from 30 to 45 mass%; and an entire vinyl bond content being from 15 to 35 mass%, the specific butadiene rubber being a butadiene rubber having a glass transition temperature of -85°C or less, wherein the glass transition temperature is measured by using a differential scanning calorimeter at a temperature elevation speed of 10 °C/min and calculated based on the midpoint method, a content of the silica being from 50 to 150 parts by mass per 100 parts by mass of the rubber component, and a content of the silane coupling agent being from 3 to 30 mass% with respect to the content of the silica.