Yes, to lie under oath (including in a deposition) is perjury. It is a felony, and could theoretically be punished by jail time--up to years in jail. But usually it is NOT prosecuted that way, because a felony perjury prosecution is expensive and can be difficult.That does *not*, however, mean that someone can lie under oath with impunity. The judge in your case can also consider this "contempt of court" and sanction your ex in any of several ways: a fine; paying some of your legal fees; some time in jail (rare but permissible); drawing an adverse inference (i.e. a negative judgment) about his testimony due to the perjury. You or your lawyer should bring this to the judge's attention.